Tutorial 5

So I made some progress towards being able to display video frames, in order to implement the tutorial.

This PR is far from complete but I'd like to get some feedback on whether it's a viable approach that's worth pursuing, or I went on a wild goose chase.

I changed the signature of the process callback to accept an &Stream, and stored the stream itself in the callback data. Then I created some wrappers and traits to get to the actual data in the pods. This way I am able to access the buffers data and metadata sections, however I have no idea how to parse them, so I stopped there.