New platform - Atari

No changes to the chess, just added an Atari version. Tested on an Atari 800 48K. The Atari version relies on NTSC color artifacts for cursor color.

Oric/C64 Graphics/CX16 versions added

New platforms - Oric/Atmos/Telestrat tape (cc65-Chess.tap), Commodore 64 Graphics version (cc65-Chess-c64.prg), the old Commodore 64 version is now the character version (cc65-Chess-chr.prg) and the Commander X16 version (cc65-Chess-cx16.prg). The Apple II DSK is unchanged, but is added here as well.

cc65 Chess V1.0 - Apple II and Commodore 64

Merge pull request #7 from oliverschmidt/master

Added a Git ignore file.