Add Moonscript support

From http://moonscript.org:

"Moonscript is a dynamic scripting language that compiles into Lua."

Re-uses the builtins from the Lua lexer.
Merge pull request #106 from nilnor/moonscript-support

Add Moonscript support
use proper style in the ruby demo
use Lexer.load_const to load sibling constants

in an idempotent way.
always reload the source in the test app

by removing the global Rouge and reloading the source manually
Fixed a typo in the README
Merge pull request #107 from elektronaut/master

Fixed a typo in the README