Add *.pyc files to Git ignore
Change way named_elem works

- Rule wouldn't properly identify single strings as named_elem, changed
it to always recognize named_elem
Add Semantic actions

- Add semantic actions for model, string and named_elem rules
- Semantic action for named_elem now returns a NamedElem metamodel class
- Add pretty print to NamedElem
Extend ModelAction to save it's name
Add semantic action for Identifier

- Renames identifier to avoid possible collisions (from id -> ident)
- Add semantic action for Identifier