Euler angles proposal

[recp]

Ken Shoemake's algorithm seems most common one, it also handles 24 different permutations of rotation order. Maybe instead of providing separate functions for euler angles we could adopt that algorithm / codes.

Related implementation (Graphics Gems IV): https://github.com/erich666/GraphicsGems/tree/master/gemsiv/euler_angle
https://github.com/erich666/GraphicsGems/blob/master/gemsiv/euler_angle/EulerAngles.c

It also provides euler to quaternion which is in our TODO list. I hope there is no any LICENSE conflict