first pass at implementing field get/set

also moved some Failure code into the .cpp file
first pass at getting tests to compile

runs 1 dummy test so far. need to add more.
start switching away from bitfields

using pragma to set the struct byte packing instead, which is better
rename qbrt/arithmetic.h -> instruction/arithmetic.h
switched all instructions to pragma byte packing

should be no more bitfields in the instructions anymore
move string instructions to instruction/string.h