We already have the convenient degrees() and radians() functions to convert
between angle formats. This commit involves a lot of refactoring here and
there and I may have missed some places where conversions were needed. But
hopefully there aren’t may such places.

The name “re” came from “reciprocal” but since we have “inverse” for
matrices, I thought it would be nice to make everything consistent.

This lets us use the code for non-float variable types. I also got
rid of the mat4-to-quat code so that users are forced to use the
mat3-to-quat code and possibly discover places where their code is
suboptimal.

Using “Array” instead of “array” is now fully deprecated, and I replaced
the Log::Debug() etc. functions with msg::debug() etc. because log:: was
unavailable due to being a maths function.

Added up-to-date copyright notice and BOM to modified files, just in case.

The containers no longer force the user to use the ptrdiff_t type for
size information. For convenience, size() now always returns an int,
and the size_s() method offers a way to handle arrays with more than
2 billion elements. Internally, we still use ptrdiff_t, though.

Since so much code had to be changed, I took the opportunity to get
rid of capitalised accessors for classes that are lowercase.

support for enable_if and other template metaprogramming techniques),
for Clang (related to static const template class member initialisation)
and for GCC (related to forward declaration of non-int enum classes).

MASK to SWIZZLE in the vector templates, rename matrix<> to mat<> for
consistency, implement transposition for all matrix sizes, make matrix
columns private and only accessible through operator[].

quaternion, improve quat::rotate(vec3, vec3) to gracefully handle corner
cases, and add unit tests for all of these.

Added workbench, for personnal experimentation.

Constants : Added minus one.

SceneSetup : Added ClearColor command
EZMesh : Added Dup[ ... ] command && cgs command syntax refactor
MViewer : Tweak & dictionnary.js updates

Camera & vector.cpp : Fixed shifted_perspective crash with almost zero FOV.