mask: use offset
asm: make "proc" synonim of "global", for partial compatibility

In all my patches "proc" was used as a first statement in block.
So it is safe to treat it as "global" synonim.
block: introduced block names in repr (untested)

To mimic behaviour of proc keyword
parser: fixed support for db HEX
Store binary data reference in Patch object, for val instruction
asm: split NullInstruction from LabelInstruction
asm: added ValInstruction (untested yet)
asm: some bugfixes for ValInstruction
test_asm: test val (not working yet)
asm: fixed some label misuse
test_asm: correct checking for val instruction
Added basic LDR Rx,lbl (buggy)
test_asm: fixed test for LDR
Added LDR Rn,[Rn{,imm}] (buggy) and test
asm: support [lists] in definitions, also in (tuples)
asm, test_asm: moved simple instructions to the end of file; also removed print stmt
Added DCD label