Improved syntax definition and snippets

Adds syntax highlighting for crate paths, methods and macro invocations.
Adds placeholder names to some of snippets.
The color scheme for the screenshot can be downloaded from [here](https://dl.dropboxusercontent.com/u/675947/Neon.tmTheme).
![screen shot 2014-03-18 at 4 39 31 am march 18](https://f.cloud.github.com/assets/1251233/2467552/34075e92-afc1-11e3-8820-0f5127de3d8e.png)