Slight polish pass

Still considering how/if I want to expand on this game, so for today just some small polish stuff:

• Added camera shake on hit/getting hit, and a slight shake while firing
• Bullets on the ground are now attracted to you in a small area
• Some particle effects on enemy hit
• Volume adjustments for several of the sounds
• The master volume in the main menu now works
• Bullets should no longer get stuck in walls
• Player should (hopefully!) not get stuck in walls while rolling