a2desktop alpha candidate

This release has the jukebox player but with:

1. The ability to quit (using ESC or Q) (pt3plr.7z)
2. Can be built into basis.system, which Bitsy Bye will call when unknown file types are selected (in this case PT3). (pt3plr-a2d.7z)

For #2 there's no error checking, the code assumes the file is a PT3 file.

basis.system does work stand-alone on a ProDOS disk, used from Bitsy Bye.

When I launch a PT3 file from Bitsy Bye:

1. $2006 contains the selected file name.
2. $0280 has the path to the file name.

When I lainch a PTR file from a2desktop,

1. $0280 contains the name of the PT3 file (no path, jsu fro example ACADEMY.PT3)

I suspect there's something I don't know about mapping file types or extensions to .system files, perhaps?