Alpha release

This version is functionnally complete : there is a transition to the start of the game, then at the end before looping back to the start of the game.

Any keyboard press quit the game, use a joystick (joystick 1, no need to unplug the mouse on real hardware)

It MAY run on any ST, but the target is Atari STE. Next releases will add some DMA audio and use blitter.