Mouse support; brighter sounds; menu polish

Several people have been asking for mouse support, so I dug in and I think I have something that works, but it could do with testing on real hardware. You need to put the mouse in port 1 - that was the path of least code, which I am extremely short of - and turn the mouse on in the options (it should autodetect and turn on automatically). Then mouse turns, and LMB shoots. Please let me know if it works, if it's too sensitive or not sensitive enough, etc.

I've never been happy with the converted pc speaker sounds. I initially just chopped 2/3 of the samples out, but that ended up missing quick pulses in the sounds, so I changed the exporter to catch and keep rising and falling edges, which improved things. PacBilly suggested using channel 2 instead of the noise channel, and the sounds immediately sounded much, much better - brighter, and closer to the original. I experimented with pulse width, triangle and sawtooth, but the default square wave couldn't be bested. Thanks PacBilly!

I also took some time to make the menu look a little better. I cleaned up the logo slightly, added a sprite based cursor, and redid the hint line at the bottom with graphical keys.

The game is updated to v1.1 and ready to download again.