Viewport Capture

[chris-luangrath]

"Easier viewport capture. The viewport capture is very useful for rl debugging, which happens a lot. Rather than be a sensor on an agent, it would probably be better if there was a environment function like env.screenshot that just captures the pixels at the current tick. Under the skin maybe it would be better for it to remain a sensor, but for the user it should be easier to access. Additionally, it would be a plus if there was a function to create easy videos/gifs with something like env.start_capture(), env.finish_capture() that creates an mp4 or at least returns a list of images."