* extend PartialRedux::cross() to any matrix sizes with automatic
vectorization when possible
* unit tests: add "geo_" prefix to all unit tests related to the
geometry module and start splitting the big "geometry.cpp" tests to
multiple smaller ones (also include new tests)
based on the former.
* opengl_demo: makes IcoSphere better (vertices are instanciated only once) and
removed the generation of a big geometry for the fancy spheres...
- quaternion vs euler angles interpolation (though the Euler angle version looks a bit too bad)
- navigation using either a mapping from 2D screen coordinates to 3D points on a sphere
or the standard approach mapping mouse displacements as rotations around camera's axes.
