Merge: Introduction of convex polygons in geometry + benchmarks

Nit implementation of the convex polygon data structure.

It's based on the java implementation done during the data structures course.

There also are benchmarks for the Nit implementation and the Java implementation to compare them

Pull-Request: #1380
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>