Added collision handler for Huayno OK algorithm

[ErwanH29]

Integrated the collision detection algorithm from the various SHARED_COLLISION Huayno integrators into the OK integrator. Note: This collision checker does not detect collisions between two massless particles.

[ErwanH29]

I made a new file which hosts the collision detection function and with which both evolve_shared_collisions.c and evolve_ok.c call. The algorithm neglects collisions between two massless particles to save computing time at the detriment that perhaps this isn't an assumption that some users would want. If that is a bother I can rewrite the code to include it.

I hope the changes are fine. I tested collisions using either integrators and I don't see a change in performance.

[rieder]

This PR needs at least a test to show that this collision detection actually works before it can be merged.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 28 days if no further activity occurs. Thank you for your contributions.