Get rid of make() and just return a dictionary instead.

It already needed special handling, and Object was being used incorrectly anyhow.
Better error reporting in mg_builtins.py
Very basic isintance support, only works for user classes
Add forgotten lex tokens
Add a Python object wrapper, so that Python functionality can be accessed directly
Use Python sets as the underlying implementation of set
Get builtin name from function name in mg_builtins
Add basic type signatures for functions