Ability to detect U-turns

[niksirbi]

It would be useful to have a function that detects U-turns in 2D based on some adjustable criterium/threshold.

I haven't though this through, but we should be able to use either compute_forward_vector or compute_displacement (or both), depending on how one defines the U-turn.

[niksirbi]

Check cout: https://traja.readthedocs.io/en/stable/turns.html#angles

[sfmig]

We discussed maybe having a detect_events module that returns an event vector. Also probably having a general version and a more specific version (similar to the head vector computation).