First draft of listfile support.

The .listfile pragma and the -l command line option will select the
output file for the listing.
add 4502 opcode table.
update addressing modes. Add 4502 to chipsets.txt
update Opcodes.py to include 4502 opcodes
add 4502 option to Ophis command line.
implement new 4510 addressing modes.
promote relative branches to 16-bit when required.
fix 16-bit branch out-by-one error
fix various bugs with 4502 assembly.
update readme to indicate 4502 support
restore branch expansion for non-4502 targets
make addressing mode cooercion work with varying addressing mode
lists.
Implement test for 4502 extensions.
Fix numerous bugs revealed through tests, some more remain.
Fix 16-bit immediate mode.
fix SBX (ZeroPage), Z for 4502
Merge pull request #19 from gardners/master

Add support for 4502/4510 CPU from Commodore 65
Post-merge adjustments to 4502 patch.
Bump minor version number and copyright dates
4502 instructions INW and DEW are Zero Page, not Absolute
Merge github.com:michaelcmartin/Ophis into temp
remove LF added during conflict resolution.