Remove private RegExp vars
Change ICompiledMode keyword to Object
Change keywords in IMode to any

The keywords key can be represented by either a string or an object, see:

http://highlightjs.readthedocs.org/en/latest/language-guide.html#keywords
Add HLJSStatic for registerLanguage use
Change registerLanguage definition to a function
No longer require begin

This is so registerLanguage parameter can return the IModeBase type, with is
essentually the language definition.