Closer and closer to release

Work could not proceed at full steam lately, but still intensive testing revealed a few things to improve/fix (that subsequently were improved/fixed, of course). Further testing will tell whether the game can be released.

CHANGELOG

• Improved last arena.
• Made a little optimization in shadows rendering.
• Fixed collision detection bug (beams were handled incorrectly).
• Fixed a recently-introduced bug in wors handling.
• Fixed a newly-introduced bug in transparent tiles handling.
• Fixed graphical quirk between soldier corpses and keys.