Add code gen for more instructions

This includes all of the arithmetic instructions.
Add make label function
Remove list of fix up instructions after fix
Add throws declaration
More improvements to DLX generation

Changed the types used for fixup maps so that functions can get labels
too. Implemented CMP, MOVE, WRITE, and WLN instructions.
Implement branch instructions
Add NoValue to serve as a placeholder
Use NoValue as place holder for Ret
Add partial implementation of Ret