[doc/book] Drop reference/policies.md and small fixes

We don't need to put `policies.md` in the book. See
<rust-lang/crates.io#1030> for more.

Renaming `introduction.md` to `index.md` prevents creating two html
files (and URL) for one source.

The rest are small styling issues.

Tracker: <#4040>

Author: behnam

src/doc/book/src/SUMMARY.md

@@ -1,6 +1,6 @@
 # Summary
 
-[Introduction](introduction.md)
+[Introduction](index.md)
 
 * [Getting Started](getting-started.md)
     * [Installation](getting-started/installation.md)
@@ -26,6 +26,5 @@
     * [Package ID Specifications](reference/pkgid-spec.md)
     * [Source Replacement](reference/source-replacement.md)
     * [External Tools](reference/external-tools.md)
-    * [Crates.io Package Policies](reference/policies.md)
 
 * [FAQ](faq.md)

src/doc/book/src/introduction.md renamed to src/doc/book/src/index.md

@@ -4,10 +4,11 @@ One of the goals of Cargo is simple integration with third-party tools, like
 IDEs and other build systems. To make integration easier, Cargo has several
 facilities:
 
-* `cargo metadata` command, which outputs project structure and dependencies
+* a `cargo metadata` command, which outputs project structure and dependencies
   information in JSON,
 
-* `--message-format` flag, which outputs information about a particular build,
+* a `--message-format` flag, which outputs information about a particular build,
+  and
 
 * support for custom subcommands.
 
@@ -85,7 +86,7 @@ Information about dependencies in the Makefile-compatible format is stored in
 the `.d` files alongside the artifacts.
 
 
-### Custom subcommands.
+### Custom subcommands
 
 Cargo is designed to be extensible with new subcommands without having to modify
 Cargo itself. This is achieved by translating a cargo invocation of the form

src/doc/book/src/reference/external-tools.md

@@ -27,14 +27,14 @@ Here, brackets indicate that the contents are optional.
 These could all be references to a package `foo` version `1.2.3` from the
 registry at `crates.io`
 
-|         pkgid                  |  name  |  version  |          url         |
-|-------------------------------:|:------:|:---------:|:--------------------:|
-| `foo`                          | foo    | *         | *                    |
-| `foo:1.2.3`                    | foo    | 1.2.3     | *                    |
-| `crates.io/foo`                | foo    | *         | *://crates.io/foo    |
-| `crates.io/foo#1.2.3`          | foo    | 1.2.3     | *://crates.io/foo    |
-| `crates.io/bar#foo:1.2.3`      | foo    | 1.2.3     | *://crates.io/bar    |
-| `http://crates.io/foo#1.2.3`   | foo    | 1.2.3     | http://crates.io/foo |
+| pkgid                        | name  | version | url                    |
+|:-----------------------------|:-----:|:-------:|:----------------------:|
+| `foo`                        | `foo` | `*`     | `*`                    |
+| `foo:1.2.3`                  | `foo` | `1.2.3` | `*`                    |
+| `crates.io/foo`              | `foo` | `*`     | `*://crates.io/foo`    |
+| `crates.io/foo#1.2.3`        | `foo` | `1.2.3` | `*://crates.io/foo`    |
+| `crates.io/bar#foo:1.2.3`    | `foo` | `1.2.3` | `*://crates.io/bar`    |
+| `http://crates.io/foo#1.2.3` | `foo` | `1.2.3` | `http://crates.io/foo` |
 
 #### Brevity of specifications
 

src/doc/book/src/reference/pkgid-spec.md

@@ -4,10 +4,11 @@ One of the goals of Cargo is simple integration with third-party tools, like
 IDEs and other build systems. To make integration easier, Cargo has several
 facilities:
 
-* `cargo metadata` command, which outputs project structure and dependencies
+* a `cargo metadata` command, which outputs project structure and dependencies
   information in JSON,
 
-* `--message-format` flag, which outputs information about a particular build,
+* a `--message-format` flag, which outputs information about a particular build,
+  and
 
 * support for custom subcommands.
 
@@ -85,7 +86,7 @@ Information about dependencies in the Makefile-compatible format is stored in
 the `.d` files alongside the artifacts.
 
 
-# Custom subcommands.
+# Custom subcommands
 
 Cargo is designed to be extensible with new subcommands without having to modify
 Cargo itself. This is achieved by translating a cargo invocation of the form

src/doc/book/src/reference/policies.md

@@ -27,14 +27,14 @@ Here, brackets indicate that the contents are optional.
 These could all be references to a package `foo` version `1.2.3` from the
 registry at `crates.io`
 
-|         pkgid                  |  name  |  version  |          url         |
-|-------------------------------:|:------:|:---------:|:--------------------:|
-| `foo`                          | foo    | *         | *                    |
-| `foo:1.2.3`                    | foo    | 1.2.3     | *                    |
-| `crates.io/foo`                | foo    | *         | *://crates.io/foo    |
-| `crates.io/foo#1.2.3`          | foo    | 1.2.3     | *://crates.io/foo    |
-| `crates.io/bar#foo:1.2.3`      | foo    | 1.2.3     | *://crates.io/bar    |
-| `http://crates.io/foo#1.2.3`   | foo    | 1.2.3     | http://crates.io/foo |
+| pkgid                        | name  | version | url                    |
+|:-----------------------------|:-----:|:-------:|:----------------------:|
+| `foo`                        | `foo` | `*`     | `*`                    |
+| `foo:1.2.3`                  | `foo` | `1.2.3` | `*`                    |
+| `crates.io/foo`              | `foo` | `*`     | `*://crates.io/foo`    |
+| `crates.io/foo#1.2.3`        | `foo` | `1.2.3` | `*://crates.io/foo`    |
+| `crates.io/bar#foo:1.2.3`    | `foo` | `1.2.3` | `*://crates.io/bar`    |
+| `http://crates.io/foo#1.2.3` | `foo` | `1.2.3` | `http://crates.io/foo` |
 
 ## Brevity of specifications