Adds support for a `CancellingInputs` instruction flag, to indicate cases like `XORQ R10, R10` where the instruction actually does not depend on the value of `R10` at all.
Closes#89
The Go assembler merges MOVD/MOVQ instruction forms. The logic in the
avo instruction loader was discarding the MOVD forms. This diff should
merge them correctly.
Updates #50
