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Bug fixes:
* Surface normal calculation for the Cone primitive was incorrect, this has been fixed.
* Parabola tip intersection case was not handled fully, this has been fixed
* Increased size of integers holding ray counts as they could overflow for extremely long renders.
New:
* Added quaternions to the core math package.
* Added low level cython functions to calculate mininum, maximum and peak_to_peak for memoryviews. (contributor: Dr Jack Lovell)
* Added a material blending modifier to the raysect.optical.material.modifiers package.relational