chore(build): documentation generation

Main changes:

* Use gulpfile now (build was getting way too disorganized with custom
tasks; gulpfiles are much easier to build clean custom tasks with than
Grunt.
* View README#Development for updated commands
* Docs written for ionContent, ionHeaderBar, ionInfiniteScroll.
* Docs are pushed to ajoslin's fork of ionic-site until they reach a
* point where they can be published.

**TODO, In Order of Priority**

1. Finish writing source-documentation for all existing components
2. Add multiple versions of docs (one per release & nightly, latest
 stable release docs being shown by default)
3. Add examples generation
4. Add searchbar to docs