Convex primitives library (e.g. hull, gjk, intersection) in plain C.

This is an extract of geometrical tools used in [Solfec] (https://github.com/tkoziara/solfec). The code includes:

• convex polytope intersection (cvi.h, tri.h)
• convex hull calculation (hul.h)
• GJK proximity tests for polytopes and ellipsoids (gjk.h)
• simplex integration (spx.h)
• approximate triangle-sphere intersection (tsi.h)
• axis aligned bounding box overlap detection (hyb.h)
• kd-tree (kdt.h)
• rb-tree based maps and sets (map.h, set.h)
• linked list sorting (lis.h)
• memory pool (mem.h)