Add experimental implementation of GtForth

[hsnaves]

This pull request contains:

• A patch to vasm.py fixing a few bugs and adding some features that are used by GtForth.vasm.py;
• An implementation of an emulator/simulator for the vCPU that can be used within Python itself;
• The source code of GtForth (together with the corresponding compiled GT1 file). The source code was written using the vasm assembler;

[hsnaves]

Well, I tested the assembler a few times, and it produces identical GT1 output files whenever the source code is compatible with both versions. And, as far as I could find, there is only one use of vasm.py in the entire repository (in Apps/Blinky/Blinky2.vasm.py).

[hnaves@blade15 gigatron-rom]$ git grep " vasm " | grep import 
Apps/Blinky/Blinky2.vasm.py:from vasm import *
Contrib/hsnaves/GtForth/GtForth.vasm.py:from vasm import *
Core/vasm.py:# SYNOPSIS: from vasm import *

I am not sure if there is any other code somewhere else... Is there any other Git repository that I am not aware of?

Regarding the move of vcpu.py, I can do that.

[hsnaves]

I forced pushed a new set of commits, to keep a clean history.

[at67]

There is no other repo that I am aware of.

Thanks for applying the change to vcpu.py.

I'll have a proper look at your changes to vasm.py tonight and merge them when I get back from work, (heading off in 3 mins), cheers.