Merge pull request #3 from Delfos1/optimizing

Optimizations, collision code, property links

v 0.6.2 Fixes

Added Orient distribution
Added Local distinction for Forces
Added Final speed function
Added exists_system and particle checks

Experiments with Normals

Also
Even Distribution collapsed into set_distribution_u and  set_distribution_v .

set_transformation() no longer has a rotation property, this is now set_stencil_offset()

Fixed other typos, names

Allowing to input several systems or particles into a single emitter (unfinished)

More fixes