* face recognition with knn

* improved knn, added doc and tests

* updated for flake8

* fixed requirements

* fixed paths in test

* fixed additional paths in test

* updated tests

* updated readme

* Add recognition with k-nearest-neighbors classifier

* Correcting for PR comments

* remove scikit-learn from global requirements

* remove scikit-learn from setup requirements

* Add intro to knn example

* Support dlib 19.7 changes

* Typo fix

* README update

Add support for dlib's new cnn-based face detector

Should capture in rgb (not bgr) format.

If `unknown_image.shape[1] > 1600` then `scale_factor` will be always calculated `0` because `1600 / unknown_image.shape[1]` is an `int` over `int` division which in turn will always raise a ValueError in `PIL.Image.resize`. Making `1600` a float (1600.0) fixes the issue.