parser: added special support for db arguments

For compatibility with old patcher
asm: added Num.ThumbExpandable mask
asm: added some MOV variants, with some tests
asm: removed debug print stmts
asm: added Num.part() to get bitwise parts of number
parser: support negative numbers
Added MOVW, fixed some tests
test_asm: rewrote eq_ for nice printing
some MOV fixes
asm: fixed ThumbExpandable for negative numbers
asm: fixed typo in Num.part

Now almost all tests pass
asm: implemented global labels
block: changed getContext() to property
block: converted getMask() to property