make available IN/OUT/PSH/POP (contributes to #9)
implement XCH (untested) (contributes to #9)
implement TFR (untested) (contributes to #9).
Set register defaults
test and fix PSH/POP (contributes to #9)
implement LDQ/LDH (closes #9)
untested addition for STEX mode (adds to #8)
implement RET/IRET (untested) (contributes to #11)
correct issue with OnboardRAM device
add shell module for 'exit' command
implement STEX mode (closes #8) and refactor some instructions
implement AND (untested) (contributes to #10)
AND tested, works (contributes to #10)
implements XOR/OR/NOT (closes #10)
add mappings to dispatch table for OR/XOR/NOT
implements MOD (tested)
Final changes for v0.2-alpha release

Signed-off-by: McSherry <liam@synaplink.net>
Merge pull request #12 from McSherry/v0.2-alpha

Merge for v0.2-alpha