add syntax highlighting for popular source file types

This PR adds syntax highlight support for many popular file extensions based on this:
https://github.com/bobbylight/RSyntaxTextArea/blob/master/src/org/fife/ui/rsyntaxtextarea/SyntaxConstants.java

Few file types that I do not know well about, are omitted. Also, the version of RSyntaxtTextArea included with Nightcode does not support all types mentioned in the `master` URL above -- those are either omitted or a fallback type has been used.