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

- 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

numpy's import_array() in a more robust way.

void*.  But the previous code didn't so it wouldn't compile.  Fixed that
problem.

* Exposed jitter_image in Python and added an example

* Return Numpy array directly

* Require numpy during setup

* Added install of Numpy before builds

* Changed pip install for user only due to security issues.

* Removed malloc

* Made presence of Numpy during compile optional.

* Conflict

* Refactored get_face_chip/get_face_chips to use Numpy as well.