Add support for API Blueprint

This adds a grammar and samples for [API Blueprint][] based on the
[Sublime Text plugin][] from Apiary. The [Atom language][] is also based
on the Sublime plugin.

API Blueprint is now used in over [3,600 repositories][] on GitHub and has
[several][Aglio] [open source][Dredd] [tools][Drakov] available.

Here's an [example using Lightshow][Lightshow] to highlight a small API.

[3,600 repositories]: https://github.com/search?utf8=%E2%9C%93&q=FORMAT+1A+extension%3Aapib+extension%3Amd&type=Code&ref=advsearch&l=
[Aglio]: https://github.com/danielgtaylor/aglio
[API Blueprint]: https://apiblueprint.org/
[Drakov]: https://www.npmjs.com/package/drakov
[Atom language]: https://github.com/danielgtaylor/atom-language-api-blueprint
[Dredd]: https://github.com/apiaryio/dredd
[Lightshow]: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_url=https%3A%2F%2Fgithub.com%2Fapiaryio%2Fapi-blueprint-sublime-plugin%2Fblob%2Fmaster%2FAPIBlueprint.tmLanguage&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fraw.githubusercontent.com%2Fapiaryio%2Fapi-blueprint%2Fmaster%2Fexamples%2F12.%2520Advanced%2520Action.md&code=
[Sublime Text plugin]: https://github.com/apiaryio/api-blueprint-sublime-plugin

samples/API Blueprint/simple.apib

@@ -0,0 +1,18 @@
+FORMAT: 1A
+
+# The Simplest API
+This is one of the simplest APIs written in the **API Blueprint**.
+One plain resource combined with a method and that's it! We will explain what is going on in the next installment - [Resource and Actions](02.%20Resource%20and%20Actions.md).
+
+**Note:** As we progress through the examples, do not also forget to view the [Raw](https://raw.github.com/apiaryio/api-blueprint/master/examples/01.%20Simplest%20API.md) code to see what is really going on in the API Blueprint, as opposed to just seeing the output of the Github Markdown parser.
+
+Also please keep in mind that every single example in this course is a **real API Blueprint** and as such you can **parse** it with the [API Blueprint parser](https://github.com/apiaryio/drafter) or one of its [bindings](https://github.com/apiaryio/drafter#bindings).
+
+## API Blueprint
++ [This: Raw API Blueprint](https://raw.github.com/apiaryio/api-blueprint/master/examples/01.%20Simplest%20API.md)
++ [Next: Resource and Actions](02.%20Resource%20and%20Actions.md)
+
+# GET /message
++ Response 200 (text/plain)
+
+        Hello World!