Use Embree for Ray Shooting

Introduction of Intel’s Embree and its applications to CGAL in the form of a package "Embree" after sufficient bench-marking. The "Embree" package makes use of the EmbreeAPI and its user-defined functionality to incorporate CGAL objects. Though in its infant stages, the Embree package has consistent declarations with CGAL::AABB_tree and is much faster in intersection and distance queries.