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.
According to asciinema.org, it should be possible to change the title
after uploading, but I couldn't figure out how to do that. Let's set
it when creating the recording. That also means it's one less step to
perform when re-running scripts.
