look_at_rh and look_at_lh mixed up

On this page:

https://www.nalgebra.org/points_and_transformations/

the methods `look_at_rh()` and `look_at_lh()` seem to be mixed up.

"A right-handed look-at view matrix that makes the z axis point toward the staring direction." The opposite is the case.

Also, `new_observer_frame` should be renamed into `face_towards`.