Layout docs landing

It’s been a long time coming, and they’re still not done, but I’ve committed some initial documentation for the Layout API. For the curious, you can access the documented classes here, there is also an introduction to building a GUI with the Layout API here. If you happen to find a typo, or inaccurate info, please contact me so I can fix it. Finally, note that, like the documentation, the Layout API is not yet finalized.