Added support for replaceable sections

This adds correct syntax highlighting for the replaceable blocks as described in
https://github.com/mustache/spec/issues/38 and implemented in Hogan.js and
mustache-java.

This turns this: 

![screen shot 2014-06-30 at 15 26 28](https://cloud.githubusercontent.com/assets/1446145/3430555/b9817f5c-0062-11e4-8079-7351826e7129.png)

Into this:

![screen shot 2014-06-30 at 15 24 21](https://cloud.githubusercontent.com/assets/1446145/3430557/bd118338-0062-11e4-8aef-d661c966f3d5.png)

Pretty simple.