AI and better looking enemies

Well, three basic AI modes are in.  I feel stupid even calling it “AI”.  It’s… behaviour.  The ships follow the player around, it’s not like it’s a thinking robot.
Anyway.  Mode one: It chases the player.  There is acceleration in all the modes (they start slow and speed up, and if they’re going fast and you get behind them, they have to slow down to turn around), but it’s hard to notice unless you set it very, very low.  I’m thinking about making it only apply to turning.
Mode two: It runs away from the player.  Not really sure what that’s good for, because they just immediately get stuck in a corner, but it took five seconds to add in, so that doesn’t really matter.
Mode three: It attempts to maintain a specific distance from the player.  The distance is hardcoded for now.  I think this mode is probably my favorite, which is why I’ve set shipdata.txt to use it for the default enemy.  Switching that value in shipdata.txt will activate the other modes.
Also, ship explosions are back in (They got lost during the conversion from pixel coords to game coords a couple updates ago, I forgot to resize the explosion size, so they were still happening, they were just much, much smaller than a pixel).  I’ve slowed down the rotation, so now they look slightly less dumb.
Retextured the enemy ships, and added orientation.

ver13