With ADDA, SUBA, and ADDQ/SUBQ when the target is an address register, the condition
flags should not be changed, but the code was changing them, which caused problems.
I've fixed it by making the ADD/SUB executions check for an address target and
will not update flags in that case. This should only occur when the actual instruction
was an ADDA or ADDQ with an address register target
The effective modes that used signed offsets were not properly
sign extending the immediate or register index values before adding
them to the address, resulting in incorrect addresses.
The flags were incorrect for some instructions, and I added the
logical shift instruction implementation
Also fixed a bug where MOVEA needs to behave differently than MOVE,
such that the data is sign extended to a long and the condition flags
are not changed. I also modifed how Addressable returns data because
I need to return owned data from MC68681, so that the stored data can
be updated (ie. the status flag must be modified after a read)
I'm using the monitor.bin binary built from computie to boot the
virtual machine, and it currently runs and loops, but there is no
actual serial device, so it's hard to tell if it's working correctly
