Add support for __PACKAGE__, __SUB__, __METHOD__ and __CLASS__

[stevan]

These should all return the names of the current package, subroutine, method or class. The $? prefixed variables will be the actual runtime objects.

[amiri]

I would like to work on a piece of this. For PACKAGE, for instance, can someone give me a hint which class to look at? Would that go in src/main/scala/org/moe/runtime/MoeRuntime.scala?

[stevan]

@amiri these values would (for the most part) be just aliases to some of the values in MoeEnvironment. The simplest way to implement them would be to make them subroutines in the CORE package, which should work fine since subroutines do not require parens.

[amiri]

Thanks, Stevan.