bugfix aabb/center & scale impls, add vec3 coercion to aabb-from-min-max, add union-box fn, add aabb unit tests
bugfix aabb/center & scale impls, add vec3 coercion to aabb-from-min-max, add union-box fn, add aabb unit tests

JDReutt/geom,thi-ng/geom,thi-ng/geom