update implementation, compare 3 implementations

matlab/RunHornSchunck.m compares:

• Matlab script HS
• Matlab Computer Vision Toolbox HS
• PyOptFlow HS

updated Python package layout and Matlab type annotation.

Packagize

Updated project layout to current Python package style.

Python >= 3.5 compatible

Uses future-fstrings module to provide backward compatibility to Python 3.5

Horn-Schunck in Pure Python

v0.1-alpha

doc