Splitted test cases in multiple files
Added javadoc
Added expression type which should be assignable for ast creation
Added assignment rules for ast creation
Optimized parser generation
Added subrules to assignable expressions
Started ast creation
Continued work on ast creation
Unfinished work...
Restarted parser
Complete rewrite

- TODO: Parser generation from AST
- TODO: Optimize generated AST
Defined Expression as common base class to all other Expressions
Added more typesafety
Added javadoc
Removed java impl try...
Complete rewrite using xtend