Added SOP algorithm to features, added Python bindings section, updated GLM path and added note to clone with --recursive.

Submodule points at release tag 0.9.8.3

I think what happened earlier is by merging the old python-bindings branch first, the pybind "upgrade" was actually a downgrade. But now it should be back to the latest.

* Now using the transparent glm bindings
* Replaced nonlinear camera estimate with the linear algorithm
* Updated RenderingParameters bindings

Adjusted RenderingParameters constructor accordingly.

This is useful to get correct angle estimates when, as in OpenCV, the viewport is upside-down.
It could maybe also be solved by negating the 2nd and 3rd row of the rotation matrix in RenderingParameters, but I couldn't get the projection right. This is probably nicer.

It still needs a more proper cleanup.

RenderingParameters gets more and more chaotic, needs a major overhaul.

Based on the affine camera estimate, and then doing SVD to obtain the closest orthonormal rotation matrix.

This is mainly to accommodate fit-model-ceres, where I've used double for all parameters

At least gcc-5.4 on Ubuntu 16.04 needs it. It shouldn't hurt on older versions.

At least gcc-5.4 on Ubuntu 16.04 needs it. It shouldn't hurt on older versions.

Careful about GLM's notation! A 3x4 matrix is a mat4x3!

Based on pybind11/eigen.h, fairly simple.
A bit of care had to be taken for matrices because glm stores the data in col-major layout in memory.
It makes an unnecessary copy of the data in glm::make_mat*, but these types are small anyway.