Adding rectangle object
Merge branch 'dev' of https://github.com/gameprez/gpdk into enhancement-#3-retangle-element

Need to update to the resent changes.
updating branch to latest changes
added rectangle.coffe to changes from dev merge
impelemented a global Collision.use_bb switch to treat all elements as rectangles, instead of a separate Rectangle element. updated collision and game code to check for use_bb switch. renamed death to destroy. renamed pathwidth and pathheight to bb_width and bb_height and added a BB() method to element class and its descendents. updated polygon and collision to use BB where appropriate
recompiled and zipped dronewar