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)

It is still added that way but the assignment in the HighlightUsages extension overrides that.  They also pass  a Gui.Document rather than a TextEditor.Document.  I don't think its ever null as everything has been initialised at that point.