Base functions

[lincior]

Adds base functions to the package:

• a Frame class to represent a video frame;
• a Reader class to wrap opencv cv2.VideoCapture
• a Writer class to wrap opencv cv2.VideoWriter that can be more easily initialised;
• a Player class that loops over videos automatically

[lincior]

It's unclear why the test that was previously successful started failing with message "Segmentation fault (core dumped)". Anyway this error is originated in the class TestWriter.

The reader object passed to Writer is passed by reference, so in principle no action is needed to de-reference this symbol as it should be garbage-collected.