Add static CollisionModel3D::create() to replace newCollisionModel3D()

Static function CollisionModel3D::create(CreateFlag) provides better
semantics over free function newCollisionModel3D(bool).
In CollisionModel3D, use CoordSpace enum instead of boolean value
Replace boolean parameter 'closest' with enum RayCollisionSearch
Minor code style fixes in <coldet.h>
coldet.h: replace 0 pointer value with NULL