Add weapons to the README

Also, rename "health cart" to "food cart"
Fix hitboxes for units.

Hitboxes are now correctly placed over sprites.
Also added XnaHelper.DrawRect(Color, Rect, SpriteBatch) as a useful visual
debugging method.
Merge branch 'hitbox_fix' of github.com:murphyslaw480/mideast-sidearm-hideaway into hitbox_fix