supercard_pro: Implement support for SCP image files
supercard_pro: Header bytes are unsigned
supercard_pro: Handle multiple revolutions correctly.
Adjust bitcell timings relative to average timing for each track.
scp: Rename from supercard_pro, and move source file to root.
Also make callsites in disk.cpp dependent on ifdef SCP
Merge pull request #16 from keirf/scp

Scp