C Logging: use instead of printf for messages

- See `--log` help message for usage.
- Supports enabling categories.
- Color severity.
- Optionally logs to a file.
- Currently use to replace printf calls in wm module.

See D3120 for details.

source/blender/python/mathutils/mathutils_Euler.c

@@ -689,8 +689,6 @@ PyDoc_STRVAR(euler_doc,
 "\n"
 "   This object gives access to Eulers in Blender.\n"
 "\n"
-"   .. seealso:: `Euler angles <https://en.wikipedia.org/wiki/Euler_angles>`__ on Wikipedia.\n"
-"\n"
 "   :param angles: Three angles, in radians.\n"
 "   :type angles: 3d vector\n"
 "   :param order: Optional order of the angles, a permutation of ``XYZ``.\n"