Xevious and Super Xevious in the next beta

I've been working on the next beta release, although it's taking a bit longer than I'd hoped, mainly because I decided to add Super Xevious as well. The next beta will include both Xevious and Super Xevious, selectable from the (very fancy) splash screen.

I still haven't gotten around to fixing up the sound; that will be next, after I finished testing the new objects introduced in Super Xevious.