Added tests (first implementation)

Usage: run nosetests2
parser: fixed description of parseBlock
tests/asm: added new tests
asm: fixed DCH
test_asm: use correct SyntaxError class
Renamed SyntaxError to ParseError to avoid clashing with python
parser: export also classes
test_asm: added tests for remaining instructions
test_asm: fixed block behaviour
test_asm: self label
test_asm: enabled BL and some fixes
asm: fixed Label.offset()
fixed BL and its test
tests: added BW, fixed B
asm: fixed B
asm: Label.offset: fixed negative offset handling
test_asm: fixed BL and BW codes
asm: fixed longJump (B.W, BL)
asm: longJump: don't use S
reverted previous commit