Euler angles support for all conventions

As I was writing python bindings for the [rs-opw-kinematics](https://github.com/bourumir-wyngs/rs-opw-kinematics) library [py-opw-kinematics](https://github.com/CEAD-group/py-opw-kinematics), I struggled with Euler angles as I wanted to support the 6 proper and 6 Tait–Bryan conventions (and both the intrinsic and extrinsic versions). I ended up porting the code from SciPy to Rust, and after plenty of headbanging and extensive testing I think I got it right.

I ended up defining a `EulerConvention` class that can convert between Euler angles, Quaternions and Rotation matrices. Would there be any interest to incorporate this functionality in the nalgebra package? I would be willing to put some work in a PR, but I would need some guidance as I am quite new to Rust.