Replaced Circle (soon to be removed from geometry.js) with Button.
Partially merged collision detection and response with rotation and friction. Removed Circle "class" and related physics methods. Various other improvements.
Added rotation and obstacles.
Some sharing in progress stuff
Added simple point-poly intersection algorithm.
Changed images (they now have outlines), obstacle json files now contain information about image width, height and offset.
Added metal_ball.png (for gravity obstacle).
Add poly-circle generation.

Poly class now can generate approximated circles. This is temporary replacement for real circle geometry.
Add metal_ball.json for gravity obstacle.
In progress stuff
Add temporary (hacky) gravity.
Add gravity gradient image.
Rename "facebookShare.png" to "facebook_share.png". Merge conflicting enable/disable functions.
Working facebook share kinda, needs few things tho
Working Facebook share with a nice small story about the game
Facebook Sharing some tweakup
Add background bodies. Fix wall generation.
Modify camera (add spring) and score text drawing.
Merge branch 'Facebook_Sharing' into Body_rotation_in_physics

* Facebook_Sharing:
  Facebook Sharing some tweakup
  Working Facebook share with a nice small story about the game
  Working facebook share kinda, needs few things tho
  Rename "facebookShare.png" to "facebook_share.png". Merge conflicting enable/disable functions.
  In progress stuff
  Some sharing in progress stuff
Rotate button image. Remove unnecessary timeout clearing in camera spring.
Revert "Rotate button image. Remove unnecessary timeout clearing in camera spring."

This reverts commit 5606154d4b379be0ee6e694dd5869318d007666c.