Make RX like graphs

Start by reviewing the RX combine-latest tutorial linked in the issue and the streamz operators that have extended tutorials. The issue names no files, tests, or entry points; a complete result would establish a way to generate execution timelines or diagrams and provide a set of examples for the generated documentation.

RX has some nice tutorials, with great graphs showing how streams get combined, eg combine latest. It would be nice if we could have these too, especially as we have extended some of the operators beyond their tutorials. Even better it would be awesome if we could generate these through the streams themselves.

One potential way to do this:

1. Attach sinks to all the nodes in question which keep track of the time when the data came through the nodes
2. Use each stream's timestamps to generate a timeline of the execution
3. Make pretty timeline? (RX is interactive, which is great but I don't know if we need that functionality) I just don't know how to do this. Tikz, matplotlib, something else?

Ideally we would create a whole bunch of these examples so we could put them in the docs. Then every time the docs are generated we could recreate them, just in case we introduce a new execution model or change the nodes (or even check to make certain that the nodes behave as we expect them to be)

@ordirules (since we were talking about this on #48)