Merge pull request #39 from murphyslaw480/master

Better Projectiles and GUI additions
camera class implemented, issue with cursor targeting requires attn
camera class implemented, issue with cursor targeting requires attn
Fixed LevelData and constructor args for weapons.
Fix weapon stuffs
Fix aiming glitch introduced by camera.

States with a camera must now call _camera.SetCameraOffset(Vector2 offset)
so the mouse location can be calculated relative to camera location.
Modify Game1 to reset input camera offset on state change