[Open Ended Evolution] Metrics

[JusteRaimbault]

We have internal metrics in mgo to measure crowding, diversity (the hitmap) in pse ; but we do not have generic measures of open-endedness, which could be useful to test benchmark pse or new algorithms. I cam across this nice paper : https://www.mitpressjournals.org/doi/full/10.1162/artl_a_00280 where they provide a consistent set of metrics with an open source implementation (in cpp though) ; we may want to implement these in mgo