Implement Tilt and UnsafeTilt converters.

Replaces #1278. Adds support for several Tilt Templates:

Safe Tilt Converters:

-  AsciiDoc
- RDoc
- Creole
- WikiCloth/MediaWiki
- Slim
- Markaby
- Radius
- Sass/SCSS
- Less
- CoffeeScript
- Builder (XML)

Unsafe Tilt Converters:

- HAML