Slack Client v2 Official Release

Original RFC: #384
v2 PR: #394

New Features

1. Client Decomposition: We’ve split the client into two.
   1. WebClient: A HTTP client focused on Slack's Web API.
   2. RTMClient: A websocket client focused on Slack's RTM API.
2. RTMClient: Completely redesigned, this client allows you to link your application's callbacks to corresponding Slack events.
3. WebClient: The WebClient now provides built-in methods for Slack's Web API. These methods act as helpers enabling you to focus less on how the request is constructed. Here are a few things that this provides:
   1. Basic information about each method through the docstring.
   2. Easy File Uploads: You can now pass in the location of a file and the library will handle opening and retrieving the file object to be transmitted.
   3. Token type validation: This gives you better error messaging when you're attempting to consume an api method that your token doesn't have access to.
   4. Constructs requests using Slack's preferred HTTP methods and content-types.

Breaking Changes:
If you're migrating from v1.x of slackclient to v2.x, Please follow our migration guide to ensure your app continues working after updating.

Check out the Migration Guide here!

v1.3.1

• Locking websocket-client version to < 0.55.0: temp fix for #385

v1.3.0

New Features

• Adds support for short lived tokens and automatic token refresh #347 (Thanks @Roach!)

Other

• update RTM rate limiting comment and error message #308 (Thanks @benoitlavigne!)
• Use logging instead of traceback #309 (Thanks @harlowja!)
• Remove Python 3.3 from test environments #346 (Thanks @Roach!)
• Enforced linting when using VSCode. #347 (Thanks @Roach!)

1.2.1

Added rate limit handling for rtm connections (thanks @jayalane!)

1.2.0

• You can now tell the RTM client to automatically reconnect by passing auto_reconnect=True

1.1.3

• Fixes Web API JSON encoding

1.1.2

• Fixed an encoding issue which was encoding some Web API params incorrectly (sorry)

1.1.1

• Adds HTTP response headers to api_call responses to expose things like rate limit info
• Moves token into auth header rather than request params

1.1.0

• Adds new SlackClientError and ResponseParseError types to describe errors - thanks @aoberoi!
• Fix Build Error (#245) - thanks @stasfilin!
• include email as user property (#173) - thanks @acaire!
• Add http reply into slack login and slack connection error (#216) - thanks @harlowja!
• Removed unused exception class (#233)
• Fix rtm_send_message bug (#225) - thanks @kt5356!
• Allow use of custom parameters on rtm_connect() (#210) - thanks @kamushadenes!
• Fix link to rtm.connect docs (#223) - @sampart!

1.0.9

Fixed rtm_send_message ID bug introduced in 1.0.8