conform to dlib's generic image interface.  This makes dealing with
numpy images in pybind11 modules much nicer.

that it's going to move the matrix into the result.

* Fixed reference count issue

* Fixed refcount issue in Python dlib.jitter_image and dlib.get_face_chips

* Consolidation of https://github.com/davisking/dlib/pull/1249

* Fixed build issue

* Fixed: Paths in a pytest file should be relative to dlib root

* Skip numpy return tests for Python 2.7 or if Numpy is not installed

* Enabled numpy returns tests on Python 2.7 using cPickle.dumps

* Fixed reference count issue

* Fixed refcount issue in Python dlib.jitter_image and dlib.get_face_chips

functions.

* Added support for variadic Python functions in find_max_global.

* Add test for find_{min,max}_global on variadic functions.

Fixed pybind11 not doing the overload resolution correctly on the cnn_face_detector's operator() in Python.

* Added set_dnn_prefer_smallest_algorithms()

* Added description for set_dnn_prefer_smallest_algorithms();w

* Changed architectures to algorithms.

- 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().

check for any exception.