entity: added refcount to prevent premature destruction of one of a group of connected entities
renderer: deactivated optimized rendering for negative scaling sprites (to allow for axis-mirroring)
renderer: added stepsize and offset for frames
bounding: added capability to detect entities that are outside the screen with an outbound vector, now used by default
bounding: optimized ellipse bounding box
actions: added drift action that lasts until the entity reaches outbound state, used by default for Enemy
gameplay improvements, fixes
- nicer default explosion
- Swing now supports center piece
- level cleanup/changes
- add dedicated test level
committed some more resources that are likely to stay to github