Asteroids RX 2023 updates

Hey guys

After finished Lunar Rescue RX I made a few updates to Asteroids RX.
- added a new game mode 'Smash' which is loosely based on the classic 'Astrosmash'

- changed the Spectrum loader so it can be more easily hacked if you want to change it or whatever. It also pauses when the game loads
- fixed a bug in the redefine keys option.

I also uploaded a newer version of the 6809 version for Dragon 32 / CoCo. Hopefully this one fixes the bugs, thanks Pere Serrat for this!