World contruction based on Edge shapes

Re-written the world contruction. previously, use circles and squares to
represent terrain. Then tried to implement polygon triangulation, but
didn't work well, too complicated for me. Instead, I try to build the
terrain using Edge shapes. Now I have implemented the destructible
terrain using Edge shapes. Right now the biggest problem is the pixmap
initialization, where I have to do pixel by pixel writing, costing a lot
of seconds of black screen on Android phone. Should fix or word around