Cleanup of Markdown Files and add CI Checking (bevyengine#1463)

I have run the VSCode Extension [markdownlint](https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint) on all Markdown Files in the Repo.
The provided Rules are documented here: https://github.com/DavidAnson/markdownlint/blob/v0.23.1/doc/Rules.md

Rules I didn't follow/fix:
* MD024/no-duplicate-heading
  * Changelog: Here Heading will always repeat.
  * Examples Readme: Platform-specific documentation should be symmetrical.
* MD025/single-title
* MD026/no-trailing-punctuation
  * Caused by the ! in "Hello, World!".
* MD033/no-inline-html
  * The plugins_guidlines file does need HTML, so the shown badges aren't downscaled too much.
* ~~MD036/no-emphasis-as-heading:~~
  * ~~This Warning only Appears in the Github Issue Templates and can be ignored.~~
* ~~MD041/first-line-heading~~
  * ~~Only appears in the Readme for the AlienCake example Assets, which is unimportant.~~

---

I also sorted the Examples in the Readme and Cargo.toml in this order/Priority:
* Topic/Folder
* Introductionary Examples
* Alphabetical Order

The explanation for each case, where it isn't Alphabetical :
* Diagnostics
  * log_diagnostics: The usage of inbuild Diagnostics is more important than creating your own.
* ECS (Entity Component System)
  * ecs_guide: The guide should be read, before diving into other Features.
* Reflection
  * reflection: Basic Explanation should be read, before more advanced Topics.
* WASM Examples
  * hello_wasm: It's "Hello, World!".

Author: MinerSebas

.github/CONTRIBUTING.md

@@ -1,4 +1,4 @@
 # Contributing
 
 Please see the [Contributing Code](https://bevyengine.org/learn/book/contributing/code/) section of
-[The Book](https://bevyengine.org/learn/book/introduction/).
+[The Book](https://bevyengine.org/learn/book/introduction/).

.github/ISSUE_TEMPLATE/bug_report.md

@@ -6,27 +6,27 @@ labels: ''
 assignees: ''
 ---
 
-**Bevy version**
+## Bevy version
 
 The release number or commit hash of the version you're using.
 
-**Operating system & version**
+## Operating system & version
 
 Ex: Windows 10, Ubuntu 18.04, iOS 14.
 
-**What you did**
+## What you did
 
 The steps you took to uncover this bug. Please list full reproduction steps if
 feasible.
 
-**What you expected to happen**
+## What you expected to happen
 
 What you think should've happened if everything was working properly.
 
-**What actually happened**
+## What actually happened
 
 The actual result of the actions you described.
 
-**Additional information**
+## Additional information
 
 Any additional information you would like to add such as screenshots, logs, etc.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -6,19 +6,19 @@ labels: ''
 assignees: ''
 ---
 
-**What problem does this solve or what need does it fill?**
+## What problem does this solve or what need does it fill?
 
 A description of why this particular feature should be added.
 
-**What solution would you like?**
+## What solution would you like?
 
 The solution you propose for the problem presented.
 
-**What alternative(s) have you considered?**
+## What alternative(s) have you considered?
 
 Other solutions to solve and/or work around the problem presented.
 
-**Additional context**
+## Additional context
 
 Any other information you would like to add such as related previous work,
 screenshots, benchmarks, etc.

.github/bors.toml

@@ -6,6 +6,7 @@ status = [
     "build-wasm (stable, ubuntu-latest)",
     "build-wasm (nightly, ubuntu-latest)",
     "build-android",
+    "markdownlint",
 ]
 
 use_squash_merge = true

.github/linters/.markdown-lint.yml

@@ -0,0 +1,3 @@
+{
+    "MD013": false
+}

.github/workflows/ci.yml

@@ -37,8 +37,8 @@ jobs:
         run: cargo fmt --all -- --check
         if: runner.os == 'linux' && matrix.toolchain == 'stable'
 
-      # type complexity must be ignored because we use huge templates for queries
-      # -A clippy::manual-strip: strip_prefix support was added in 1.45. we want to support earlier rust versions
+      # -A clippy::type_complexity: type complexity must be ignored because we use huge templates for queries.
+      # -A clippy::manual-strip: strip_prefix support was added in 1.45. We want to support earlier rust versions.
       - name: Clippy
         run: cargo clippy --all-targets --all-features -- -D warnings -A clippy::type_complexity -A clippy::manual-strip
         if: runner.os == 'linux' && matrix.toolchain == 'stable'
@@ -80,3 +80,20 @@ jobs:
         run: cargo install cargo-apk
       - name: Build APK
         run: cargo apk build --example android
+
+  markdownlint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          # Full git history is needed to get a proper list of changed files within `super-linter`
+          fetch-depth: 0
+
+      - name: Run Markdown Lint
+        uses: github/super-linter@v3
+        env:
+          VALIDATE_ALL_CODEBASE: false
+          VALIDATE_MARKDOWN: true
+          DEFAULT_BRANCH: master
+          # Not needed here as only one Linter is used.
+          #GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

CHANGELOG.md

@@ -1,3 +1,6 @@
+<!-- MD024 - We want repeated headings in a changelog file -->
+<!-- markdownlint-disable-file MD024 -->
+
 # Changelog
 
 While we try to keep the `Unreleased` changes updated, it is often behind and does not include
@@ -6,16 +9,16 @@ current changes on git with [previous release tags][git_tag_comparison].
 
 [git_tag_comparison]: https://github.com/bevyengine/bevy/compare/v0.4.0...main
 
-
 ## Version 0.4.0 (2020-12-19)
 
 ### Added
+
 - [add bevymark benchmark example][273]
-- [gltf: support camera and fix hierarchy][772] 
+- [gltf: support camera and fix hierarchy][772]
 - [Add tracing spans to schedules, stages, systems][789]
 - [add example that represents contributors as bevy icons][801]
 - [Add received character][805]
-- [Add bevy_dylib to force dynamic linking of bevy][808] 
+- [Add bevy_dylib to force dynamic linking of bevy][808]
 - [Added RenderPass::set_scissor_rect][815]
 - [`bevy_log`][836]
   - Adds logging functionality as a Plugin.
@@ -33,7 +36,7 @@ current changes on git with [previous release tags][git_tag_comparison].
   - Replaces the properties system
 - [Add support for Apple Silicon][928]
 - [Live reloading of shaders][937]
-- [ Store mouse cursor position in Window][940]
+- [Store mouse cursor position in Window][940]
 - [Add removal_detection example][945]
 - [Additional vertex attribute value types][946]
 - [Added WindowFocused event][956]
@@ -46,9 +49,9 @@ current changes on git with [previous release tags][git_tag_comparison].
 
 ### Changed
 
-- [delegate layout reflection to RenderResourceContext][691] 
+- [delegate layout reflection to RenderResourceContext][691]
 - [Fall back to remove components one by one when failing to remove a bundle][719]
-- [Port hecs derive macro improvements][761] 
+- [Port hecs derive macro improvements][761]
 - [Use glyph_brush_layout and add text alignment support][765]
 - [upgrade glam and hexasphere][791]
 - [Flexible ECS Params][798]
@@ -242,7 +245,7 @@ current changes on git with [previous release tags][git_tag_comparison].
 - [`FrameTimeDiagnosticsPlugin` now shows "frame count" in addition to "frame time" and "fps"][678]
 - [Add hierarchy example][565]
 - [`WgpuPowerOptions` for choosing between low power, high performance, and adaptive power][397]
-- Derive `Debug` for more types: [#597][597], [#632][632] 
+- Derive `Debug` for more types: [#597][597], [#632][632]
 - Index buffer specialization
   - [Allows the use of U32 indices in Mesh index buffers in addition to the usual U16 indices][568]
   - [Switch to u32 indices by default][572]
@@ -286,7 +289,7 @@ current changes on git with [previous release tags][git_tag_comparison].
 - [Migrated to Rodio 0.12][692]
   - New method of playing audio can be found in the examples.
 - Added support for inserting custom initial values for `Local<T>` system resources [#745][745]
-  
+
 ### Fixed
 
 - [Properly update bind group ids when setting dynamic bindings][560]
@@ -359,7 +362,6 @@ current changes on git with [previous release tags][git_tag_comparison].
 [745]: https://github.com/bevyengine/bevy/pull/745
 [752]: https://github.com/bevyengine/bevy/pull/752
 
-
 ## Version 0.2.1 (2020-9-20)
 
 ### Fixed

CREDITS.md

@@ -5,14 +5,14 @@
 * hecs
 * legion_transform
 * wgpu-rs examples
-* yaks: ArchetypeSet, borrowed some ideas from their scheduler implementation 
+* yaks: ArchetypeSet, borrowed some ideas from their scheduler implementation
 
 ## Inspiration
 
 * game engines: amethyst, coffee
-* ecs: legion, shipyard, yaks 
+* ecs: legion, shipyard, yaks
 
 ## Assets
 
 * Generic RPG Pack (CC0 license) by [Bakudas](https://twitter.com/bakudas) and [Gabe Fern](https://twitter.com/_Gabrielfer)
-* Environment maps (`.hdr` files) from [HDRIHaven](https://hdrihaven.com) (CC0 license)
+* Environment maps (`.hdr` files) from [HDRIHaven](https://hdrihaven.com) (CC0 license)