* 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.

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.

This fixes the constexpr bug with VS2015U3

* Added estimate_orthographic_camera inside the submodule "fitting", and also added bindings for RenderingParameters
* Updated documentation a bit

This allows buffer objects (e.g. arrays) to be converted to eos.Mat (and eos.VecXf), which will then subsequently be converted to cv::Mat/cv::VecXf in C++.
Added mostly support for 1-channel CV_32F and CV_64F types.
The explicit conversion that's required in Python is a bit cumbersome, but I can live with it for now.

Put things from the morphablemodel namespace in a python submodule.

This adds a Python buffer view to cv::Vec4f, and the type is exposed as eos.Vec4f.
That means that the type is convertible to a NumPy array using `np.array(vec4f_instance)`.

Also renamed the app that creates the bindings to generate-python-bindings.cpp.

- Added a flag GENERATE_PYTHON_BINDINGS to CMake which enables the use of pybind11
- `create-python-bindings` generates bindings for PcaModel
- pybind11 is added as a submodule; needs to be cloned with `git submodule update --init`
- Increased cmake_minimum_required to 2.8.12 for pybind11

Changed all affected functions and classes accordingly: Mainly the renderer, affine-renderer, and affine texture extraction.

This results in a ~35% speed-up of rendering meshes.

It requires some not-so-beautiful conversions in render_affine and the current texture extraction, but they will be superseded by the new renderer soon anyway.

Fits camera, shape, blendshapes and colour coefficients with a cost function containing a landmark constraint, priors, and minimising the error between the input image's RGB values and the model estimate (rendered at each vertex).

Note: The image cost function cannot be used with the model on GitHub, as it doesn't include the colour PCA.