language.

CodeGenerator:
* modify to track stack depth
* add emit method that call's PythonVMCode's makeCodeObject
* thread filenames through in hackish way
* set flags for code objects for modules and functions
  XXX the docs for the flags seem out of date and/or incomplete

PythonVMCode:
* add doc string describing the elements of a real code object

LineAddrTable:
* creates an lnotab (no quite correctly though)