Refactor to use custom compositor-like structure

:warning: Not ready for merge.

This is a middle ground between #2 and master. 

Rather than dealing with tracks and export sessions and weird unknown errors, this implementation is going to do a lot of the under-the-hood stuff manually. 

Now that I have a pretty good understanding of the abilities of `CMSampleBuffer` and AVFoundation in general I can use it to its advantage while gaining the experience of really working with the nitty-gritty. 

The idea is to use an interface that will very much remind people of `AVVideoCompositing` to maintain the ability of easily dropping in any interpolation algorithm.