Finish work on "Method body" Closed #7. Initial draft of issue #8, very basic constant expressions.
Issue #9. Some arithmetic and logic operators implemented.
Most of operators implemented. Field/Attribute access, instanceof, cast, bitwise, power… Closed #9 #8 #7. There is some issues with location, so it's ignored now.
Closed #7 #8 #9. Method bodies, operators, statements & expressions.

Merge branch 'feature/method_body' into develop.
Make ast writing to xml optional. Disabled via static field.