Add mathutils.bvhtree API

Originally D966 by @lukastoenne, with own additions

- trees can be initialized from Object's, BMesh,
  or passed in as vert+polygon arrays.
- original indices of ngons/faces are used. (instead of tessellated indices).
- ray_cast, find_nearest methods
- find overlapping faces between 2 trees

source/blender/python/mathutils/mathutils.c

@@ -600,6 +600,7 @@ static struct PyModuleDef M_Mathutils_module_def = {
 #include "mathutils_geometry.h"
 #include "mathutils_interpolate.h"
 #ifndef MATH_STANDALONE
+#  include "mathutils_bvhtree.h"
 #  include "mathutils_kdtree.h"
 #  include "mathutils_noise.h"
 #endif
@@ -653,6 +654,11 @@ PyMODINIT_FUNC PyInit_mathutils(void)
 	PyDict_SetItemString(sys_modules, PyModule_GetName(submodule), submodule);
 	Py_INCREF(submodule);
 
+	/* BVHTree submodule */
+	PyModule_AddObject(mod, "bvhtree", (submodule = PyInit_mathutils_bvhtree()));
+	PyDict_SetItemString(sys_modules, PyModule_GetName(submodule), submodule);
+	Py_INCREF(submodule);
+
 	/* KDTree submodule */
 	PyModule_AddObject(mod, "kdtree", (submodule = PyInit_mathutils_kdtree()));
 	PyDict_SetItemString(sys_modules, PyModule_GetName(submodule), submodule);