the Python API.

normalize_image_gradients(), line, signed_distance_to_line(),
distance_to_line(), reverse(), intersect(), count_points_on_side_of_line(),
count_points_between_lines(), dot(), and normalize() to Python API.

- Moved all uses of PYBIND11_MAKE_OPAQUE to a common header to avoid possilbe ODR violations.
- Added python binding for make_bounding_box_regression_training_data().

* Replace boost::python with pybind11

* Replace add_python_module with pybind11_add_module

* Fix clang error on type-dependent expression

Can either be a list of full_object_detections or a single
full_object_detection. I couldn't get the vector type to work
for full_object_detection due to a template error.

Also, move the vectorize template into its own header to
stop having to declare it again in vector.

Also, change point x and y to be properties

#include statements to reflect this move.

--HG--
rename : tools/python/src/boost_python_utils.h => dlib/python/boost_python_utils.h
rename : tools/python/src/pyassert.h => dlib/python/pyassert.h
rename : tools/python/src/serialize_pickle.h => dlib/python/serialize_pickle.h