Updatelog

Improved collision persistance.
- Completely reworked the hash map implementation.
- Fixed SHG losing collision persistance. However this affects the performance.
- New nv_Space.collision_persistance attribute defines the number of frames a collision resolution stays alive for.
New methods nv_Space_remove & nv_Space_kill
Added kill boundaries (nv_Space.kill_bounds & nv_Space.use_kill_bounds).
New examples: varying_friction.c and domino.c
Matrix API has been refactored and moved to its own header.
Improved docs.
Better platform detection in nova_builder.py build script.

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