Implemented try/catch semantics.

-Changed primitive procedure signature to return flag instead of
 procecure result (results are pushed to stack explicitly).

-Compiler supporting local var assingment

-On exception frames, using imodule index to access the exception class
 -- no more exception_types section on mmc.

-Using extra register bp to access cp through the frames in the stack

-Note: compilation of try/catch on meme_tr.g is quite hacky

Closes #116