Initial implementation of language aliases.

To do:

- fix other build types
- check if pre-compressed build yields identical result
- add docs for registerLanguage, getLanguage
- document removal of LANGUAGES
Using "language-js" in the aliases test. Just for fun!
Added aliases for xml and cpp.
Using registerLanguage in the Node build.
Documentation for aliases.

registerLanguage, getLanguage, aliases in classref.txt
Removed erroneous space in wrap_language.
Merge branch 'aliases'

Conflicts:
	src/highlight.js