Raysect

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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

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API Changes:
* LoggingRay now logs the full intersection object, not just the hit point.

Bug fixes:
* Fixed recursive call bug triggered by inspecting the process attribute of MulticoreEngine.
* Added zip_safe=False to setup.py as installing Raysect as a zip file prevents access to cython .pxd files.

New:
* Improved behaviour of pipeline displays when raysect used in a jupyter notebook.
* Added ability to directly sample the BSDF of ContinuousBSDF materials.
* Added to_cylindrical and from_cylindrical coordinate system conversion functions.
* All spectral functions are now callable. Calling a spectral function evaluates it at the specified wavelength.

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Bug Fixes:
* Spectrum class samples attribute is now publically accessible again, not readonly.

New:
* Optimised materials significantly by avoiding unnecessary memoryview creation, ~10-20% speedups depending on material.
* Optimised observers leading to less overhead per pixel.
* Added caching to 2D mesh interpolator evaluations.

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Bug Fixes:
* Mesh load() not correctly populating vertex and triangle data arrays.
* Missing import guard for OpenCV camera, users no longer forced to install OpenCV!
* VTK importer no longer crashes when mesh name is None.

New:
* Pickle support added to all scenegraph objects. It is now possible to pickle a scenegraph.
* Mesh normals can be flipped during import/creation with new flip_normals argument.
* Optimised ImportanceManager gaining a 7% speedup for Cornell Box test case.
* Optimised method call in optical.Ray gaining a 2% speedup for Cornell Box test case.

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API Changes:
* Etendue replaced with sensitivity in the observers. [202]

Bug Fixes:
* Raysect now builds with Cython 0.28.
* Fixed pixel geometry changes not triggering a recalculation of the TargettedCCD pixel sensitivity. [219]

New:
* Added MeshCamera. A camera that uses the triangles of a mesh as pixels. [204]
* Added Spectral and Monochromatic 1D pipelines. [supporting 204]
* Added STL and OBJ mesh exporters. [176]
* Added limited support for PLY and VTK mesh importing/exporting. [209, 224]
* Added OpenCV camera. [109]
* Added sub-sampling (anti-aliasing) to VectorCamera. [222]
* Added masked samplers that allow users to limit the region being rendered. [223]
* Added meta dictionary attribute to scene-graph nodes to allow users to attach their own data. [218]
* Added is_identity() and is_close() comparison methods to AffineMatrix3D. [199]
* Added angle() to vector objects to compute angle between vectors. [205]

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Bug Fixes:
* setup.py broke installation in pip.