Step Inititialization (#2)

## Basics
This step uses the [expo-cli](https://docs.expo.io/versions/latest/introduction/installation#local-development-tool-expo-cli) to create Xcode and Android Studio projects for your app.

## Eject Method
- If you use any Expo SDK you must to provide username and password for your Expo account.
Because in this case, the expo-cli will use the expoKit eject method which needs an account.

- If your project does not import any Expo SDK then you should not use the username/password option.
Because in this case, the expo-cli will use the plain eject method.

.gitignore

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+.bitrise*
+_tmp

Gopkg.toml

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+[[constraint]]
+  branch = "master"
+  name = "github.com/bitrise-io/go-utils"
+
+[[constraint]]
+  branch = "master"
+  name = "github.com/bitrise-tools/go-steputils"
+
+[prune]
+  go-tests = true
+  unused-packages = true

README.md

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+# [Beta] Expo Detach
+
+Using the The Expo Development CLI to Creates Xcode and Android Studio projects for your app.
+
+
+## How to use this Step
+
+Can be run directly with the [bitrise CLI](https://github.com/bitrise-io/bitrise),
+just `git clone` this repository, `cd` into it's folder in your Terminal/Command Line
+and call `bitrise run test`.
+
+*Check the `bitrise.yml` file for required inputs which have to be
+added to your `.bitrise.secrets.yml` file!*
+
+Step by step:
+
+1. Open up your Terminal / Command Line
+2. `git clone` the repository
+3. `cd` into the directory of the step (the one you just `git clone`d)
+5. Create a `.bitrise.secrets.yml` file in the same directory of `bitrise.yml`
+   (the `.bitrise.secrets.yml` is a git ignored file, you can store your secrets in it)
+6. Check the `bitrise.yml` file for any secret you should set in `.bitrise.secrets.yml`
+  * Best practice is to mark these options with something like `# define these in your .bitrise.secrets.yml`, in the `app:envs` section.
+7. Once you have all the required secret parameters in your `.bitrise.secrets.yml` you can just run this step with the [bitrise CLI](https://github.com/bitrise-io/bitrise): `bitrise run test`
+
+An example `.bitrise.secrets.yml` file:
+
+```
+envs:
+- A_SECRET_PARAM_ONE: the value for secret one
+- A_SECRET_PARAM_TWO: the value for secret two
+```
+
+## How to create your own step
+
+1. Create a new git repository for your step (**don't fork** the *step template*, create a *new* repository)
+2. Copy the [step template](https://github.com/bitrise-steplib/step-template) files into your repository
+3. Fill the `step.sh` with your functionality
+4. Wire out your inputs to `step.yml` (`inputs` section)
+5. Fill out the other parts of the `step.yml` too
+6. Provide test values for the inputs in the `bitrise.yml`
+7. Run your step with `bitrise run test` - if it works, you're ready
+
+__For Step development guidelines & best practices__ check this documentation: [https://github.com/bitrise-io/bitrise/blob/master/_docs/step-development-guideline.md](https://github.com/bitrise-io/bitrise/blob/master/_docs/step-development-guideline.md).
+
+**NOTE:**
+
+If you want to use your step in your project's `bitrise.yml`:
+
+1. git push the step into it's repository
+2. reference it in your `bitrise.yml` with the `git::PUBLIC-GIT-CLONE-URL@BRANCH` step reference style:
+
+```
+- git::https://github.com/user/my-step.git@branch:
+   title: My step
+   inputs:
+   - my_input_1: "my value 1"
+   - my_input_2: "my value 2"
+```
+
+You can find more examples of step reference styles
+in the [bitrise CLI repository](https://github.com/bitrise-io/bitrise/blob/master/_examples/tutorials/steps-and-workflows/bitrise.yml#L65).
+
+## How to contribute to this Step
+
+1. Fork this repository
+2. `git clone` it
+3. Create a branch you'll work on
+4. To use/test the step just follow the **How to use this Step** section
+5. Do the changes you want to
+6. Run/test the step before sending your contribution
+  * You can also test the step in your `bitrise` project, either on your Mac or on [bitrise.io](https://www.bitrise.io)
+  * You just have to replace the step ID in your project's `bitrise.yml` with either a relative path, or with a git URL format
+  * (relative) path format: instead of `- original-step-id:` use `- path::./relative/path/of/script/on/your/Mac:`
+  * direct git URL format: instead of `- original-step-id:` use `- git::https://github.com/user/step.git@branch:`
+  * You can find more example of alternative step referencing at: https://github.com/bitrise-io/bitrise/blob/master/_examples/tutorials/steps-and-workflows/bitrise.yml
+7. Once you're done just commit your changes & create a Pull Request
+
+
+## Share your own Step
+
+You can share your Step or step version with the [bitrise CLI](https://github.com/bitrise-io/bitrise). If you use the `bitrise.yml` included in this repository, all you have to do is:
+
+1. In your Terminal / Command Line `cd` into this directory (where the `bitrise.yml` of the step is located)
+1. Run: `bitrise run test` to test the step
+1. Run: `bitrise run audit-this-step` to audit the `step.yml`
+1. Check the `share-this-step` workflow in the `bitrise.yml`, and fill out the
+   `envs` if you haven't done so already (don't forget to bump the version number if this is an update
+   of your step!)
+1. Then run: `bitrise run share-this-step` to share the step (version) you specified in the `envs`
+1. Send the Pull Request, as described in the logs of `bitrise run share-this-step`
+
+That's all ;)
+
+## Trigger a new release
+
+- __merge every code changes__ to the `master` branch
+- __push the new version tag__ to the `master` branch

bitrise.yml

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+format_version: 5
+default_step_lib_source: https://github.com/bitrise-io/bitrise-steplib.git
+
+app:
+  envs:
+  - BITRISE_STEP_GIT_CLONE_URL: https://github.com/bitrise-steplib/steps-expo-detach.git
+
+  # Define it in .bitrise.secrets.yml
+  - USER_NAME: $USER_NAME
+  - PASSWORD: $PASSWORD
+
+workflows:
+  test:
+    envs:
+    - ORIGIN_SOURCE_DIR: $BITRISE_SOURCE_DIR
+    - SAMPLE_APP_URL: https://github.com/bitrise-samples/react-native-expo.git
+    before_run:
+    - audit-this-step
+    steps:
+    - go-list:
+    - golint:
+    - errcheck:
+    - go-test:
+    after_run:
+    - plain
+    - expo_kit
+    - plain_2_0_0
+    - expo_kit_2_0_0
+
+  plain:
+    before_run:
+    - _clear_workdir
+    steps:
+    - script:
+        title: Clone sample app
+        inputs:
+        - content: git clone $SAMPLE_APP_URL . && cd
+    - [email protected]:
+        title: Install node modules for the expo project
+        inputs:
+        - command: install
+    - path::./:
+        title: Step Test
+        run_if: true
+        inputs:
+        - project_path: $BITRISE_SOURCE_DIR
+        - expo_cli_verson: "latest"
+
+  plain_2_0_0:
+    before_run:
+    - _clear_workdir
+    steps:
+    - script:
+        title: Clone sample app
+        inputs:
+        - content: git clone $SAMPLE_APP_URL . && cd
+    - [email protected]:
+        title: Install node modules for the expo project
+        inputs:
+        - command: install
+    - path::./:
+        title: Step Test
+        run_if: true
+        inputs:
+        - project_path: $BITRISE_SOURCE_DIR
+        - expo_cli_verson: "2.0.0"
+
+  expo_kit:
+    before_run:
+    - _clear_workdir
+    steps:
+    - script:
+        title: Clone sample app
+        inputs:
+        - content: git clone -b expo_sdk $SAMPLE_APP_URL . && cd
+    - [email protected]:
+        title: Install node modules for the expo project
+        inputs:
+        - command: install
+    - path::./:
+        title: Step Test
+        run_if: true
+        inputs:
+        - project_path: $BITRISE_SOURCE_DIR
+        - expo_cli_verson: "latest"
+        - user_name: $USER_NAME
+        - password: $PASSWORD
+
+  expo_kit_2_0_0:
+    before_run:
+    - _clear_workdir
+    steps:
+    - script:
+        title: Clone sample app
+        inputs:
+        - content: git clone -b expo_sdk $SAMPLE_APP_URL . && cd
+    - [email protected]:
+        title: Install node modules for the expo project
+        inputs:
+        - command: install
+    - path::./:
+        title: Step Test
+        run_if: true
+        inputs:
+        - project_path: $BITRISE_SOURCE_DIR
+        - expo_cli_verson: "2.0.0"
+        - user_name: $USER_NAME
+        - password: $PASSWORD
+
+  _clear_workdir:
+    envs:
+    steps:
+    - script:
+        inputs:
+        - content: |-
+            #!/bin/bash
+            set -ex
+            cd ${ORIGIN_SOURCE_DIR}
+            rm -rf "./_tmp"
+            mkdir "_tmp"
+    - change-workdir:
+        title: Switch working dir to test / _tmp dir
+        description: |-
+          To prevent step testing issues, like referencing relative
+          files with just './some-file' in the step's code, which would
+          work for testing the step from this directory directly
+          but would break if the step is included in another `bitrise.yml`.
+        run_if: true
+        inputs:
+        - path: ${ORIGIN_SOURCE_DIR}/_tmp
+        - is_create_path: true
+
+  # ----------------------------------------------------------------
+  # --- workflows to Share this step into a Step Library
+  audit-this-step:
+    steps:
+    - script:
+        inputs:
+        - content: |-
+            #!/bin/bash
+            set -ex
+            stepman audit --step-yml ./step.yml