General:
 - (kempston) JOYSTICK emulation
 - better keyboard handling
 - add z80 emulation and screen handling in C
 - recognize more snapshot formats

X:
 - Tcl/Tk user interface
 - (even) better color allocation
 - better z80_mem -> image conversion (1 phase instead of 2 phases)
 - monochrome displays

VGA:
 - on screen menus
