Add crystal

Add crystal lang ( http://crystal-lang.org/ )

• add demo/crystal
• copy lexer from ruby with some adjustements

### adjustements

• typeof, etc are keywords
• enum and struct are keywords (should it be builtins ?)

Added 1 commit:

• e710712d - add keyword "of"

Added 1 commit:

• acb263bb - rename crystal demo "crystal.cr" to "crystal"

Added 1 commit:

• 2f76b170 - add some keywords to crystal