Error fixed: Setting xOff to 'center' would force yOff 'center'
Example theme now uses flat ressource format instead of old (non-working) tree-based format
Major improvements to collision detection:
- Masks and bounding boxes are now pregenerated on engine startup (for small images)
  - Much more precise bounding boxes
  - No unnecessary mask generation each time objects using the same sprite are spawned
- Mask and bounding boxes can now be drawn above the collidable objects, for debugging purposed, by setting the following engine options to true:
  - "drawMasks"
  - "drawBBoxes"
Example showing the mask and bbox drawing features has been added