version 0.5: moving enemies, some fixes

* waits a sec at level display (in case of accidental keypress)
* moving enemies (move up+down)
# bullets removed correctly so they can be used again later
* first level made
# enemy weaponfire is fired from correct positions
+ your ship explodes on impact with ships/bullets
* game over screen will be displayed just *after* your ship's gone
+ frame counter onscreen