The demos don't need to be animated - the user wouldn't miss anything
if they skipped to the end. So let's just show the full output so the
user can read through it at their own pace. We could use plain text,
but I think the colors are helpful, so I went with screenshots.
Closes#166.
It can take quite a while to record a demo. This patch adds a `--fast`
flag for reducing delays to a tenth of the usual. You can play the
recording with `asciinema play -s 0.1` to get close-to-normal speed
(except that command delays will be slower). That way you can adjust
timings with shorter round-trips.
