Add goto command.
Add goto command.

It's actually a subroutine call, but that's really an implementation detail.
You should really use the SBREAK instruction to return to the debugger.
Note: neither VASM nor E supports SBREAK at the moment, but plans are afoot.

Fixes #65

8l/kestrel,KestrelComputer/kestrel,KestrelComputer/kestrel,KestrelComputer/kestrel,sam-falvo/kestrel,8l/kestrel,sam-falvo/kestrel,8l/kestrel,sam-falvo/kestrel,8l/kestrel,KestrelComputer/kestrel,8l/kestrel,sam-falvo/kestrel,8l/kestrel