Fixed last commit, added helper functions for glm/Mat and get_4x4_modelview_matrix(fitting::OrthographicRenderingParameters

Wrapped the extraction of a triangle in a lambda and calling all lambdas with std::async

At the moment, only TextureInterpolation::NearestNeighbour is adjusted to work

- extended TriangleToRasterize
- process_prospective_tri()
- added plane class
- added clip_polygon_to_plane_in_4d()

Moved affine-specific rendering to render_affine_detail.hpp, added raster_triangle() for the generic case

Set version to 0.

To facilitate this, added a get_texture_coordinates() method to MorphableModel

Also updated the documentation of Mesh.

Additionally: Using '//' for the forward declarations so they don't get picked up by doxygen

- We now use the same values and formulas as in Smith & Aldrian for the detector 2D variance.
- This changes the ranges of values a bit, so set an equivalent reasonable regularisation default value

Changed the detector variance in the shape fitting from clip-coords to image-coords. This makes the regularisation behave normal again.

Also chose a slightly higher regularisation value to stay a bit closer to the mean face by default.

Added an extract_texture overload that works without supplying a depthbuffer - it should be the default function to use.