Changed the implementation of RLTK::Parser::State#each

This allows proper modification of the @items collection while iterating in Rubinius
Added RLTK::Parser#each_state to iterate over the @states collection

This allows modification of the collection while iterating over it. Fixes an issue with Rubinius.
Merge branch 'master' of git://github.com/benedikt/RLTK into benedikt-master

Conflicts:
	lib/rltk/parser.rb