WIP: method invocation

Punting on this for a bit b/c the error messages are totally illegible,
going to do toString first so we can see wtf is going on.
Interpreter: Raises error if asked for value after its finished
Merge branch 'method-invocation' -- but remove its work

Does nothing, b/c I'm changing the implementation. But wanted to get it
merged os I wouldn't lose the commit.

Conflicts:
	interpreter/src/ruby/RubyInterpreter.hx
	interpreter/src/ruby/ds/EvaluationState.hx
Interpreter: Interprets String