A First step towards better syntax highlighting

This is the first stage of better syntax highlighting. It currently handles greying out blocks that are conditionally compiled out, multiline block comments and multiline strings, as well as highlighting of classes. Comments and criticisms welcome. 

Has not been testing on OS/X, but has been tested on Windows.

See below screenshot for an example: 

![image](https://cloud.githubusercontent.com/assets/1762752/4013831/7a2c0200-2a1a-11e4-86c4-d11886cad04a.png)

In C# the Gui.Document is always passed in as part of Highlight usages initialisation.  Thats the approach I used when trying it out.