v0.6.0: OpenGL-like rendering, texture rendering, texture extraction view-angle computation

fit-model: Replaced affine camera estimation with nonlinear algorithm (allows direct recovery of the pose angles)

This should make the app easier to understand, i.e. remove anything that's not necessary.

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

Added OpenCV 3.0 compatibility to the examples with an if/else in CMakeLists

imread has moved from highgui to the imgcodecs module in version 3.0.

- 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

imread has moved from highgui to the imgcodecs module in version 3.0.

Set version to 0.

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

Clarified installation instructions for the header include paths