Added StreamFeed class to represent data coming in from a live stream. Fakes a stream by just reading through a video file.

Creates a subprocess to read through the stream, and sends data over a
pipe to the main process.
stopped from being able to start stream twice / added better comments
Switched StreamFeed.GetFrame() to return a (ret,frame) pair like cap
instead of just the frame
separated out the frame delay into a variable
Merge branch 'live_stream_feed': Added a StreamFeed class that provides asynchronous access to the video's frames.

For now, at least, it just plays the loaded video in a separate process, and so whenever you ask it for the current
frame, it provides the latest frame from that other process. In the future, though, instead of just playing a video
from file, the frames could come from an actual stream. The class can/should be refactored to make that behavior a
subclass, but for now there's no reason.

So basically it's just a class that plays a video at a given framerate, and then you can query it for frames.
It's cool because it let's you see how well your code would work on a live stream.