Added XL programming language (http://xlr.sf.net and http://www.taodyne.com)
Merge branch 'master' of github.com:c3d/highlight.js into xl

Conflicts:
	AUTHORS.en.txt
	docs/css-classes-reference.rst
	src/test.html
Moving the note about XL in CHANGES.md to the current version.
Adding Christophe de Dinechin to AUTHORS.ru.txt
Structural fixes to xl.js.

- Changed keyword-style modes into keywords.
- Reset relevances.
- Used beginKeywords for imports and actually included imports in the language's
  "contains".
Reindenting xl.js with two spaces.