Update 0.2.0: Level Themes, Text Effects, More Artifacts

This update was three days in the making instead of the usual one. However, as this project progresses, it takes longer and longer to add features, both because I spend more time testing the game than building it and because the complexity of the code has only gone up. With that in mind, here's the changes:

• added a sound for bullets hitting walls
• added 13 more wall types and particle types for them
• added 5 more artifacts
• added 3 more weapons, some are binary fire
• chests can't spawn inside doors anymore
• fixed a critical bug with final enemies messing up the camera
• expanded level generation flexibility to allow many different themes of levels to be made
• used aforementioned level generation to change the layout of the games levels, theres now 4 of them, each themed after one of the colors so far.
• added some pitch variety to lots of sounds
• enemies no longer try to path around each other to shoot you, if they can. 
• added a text display system, used it to have pickup displays for ammo and health, as well as show some damage numbers when you get hit and show when you've successfully dodged a bullet.
• fixed a stupid bug with chest generation
• made an exit condition for door generation if its taking too long
• turned phy_bullet back on
• addressed some serious memory leaks in the particle system
• lots of small adjustments to sprites for player, enemies, and bullets