Specialized assignment instructions

[darrylabbate]

Depends on:

• #49

Opcode	Operand(s)	Operation
SETG	X	globals[K[X]] = SP[-1]
SETL	X	FP[X] = SP[-1]

This can also be extended as a binary op with an extra operand, but it's unclear if this is a good idea since I want to extend any optimzations to compound assignment as well - so there may not be enough space for all the extra opcodes.