Allow user to compete with self

[chikamichi]

Add an option to replicate own typing rythm entirely, allowing for self-replay.

[chikamichi]

• Map key strokes to a replay$ stream, with timestamps and type (nb_tick, error, etc.)
• Display replay using the top-line, which should progress or stop and change color during errors.

[chikamichi]

See https://stackoverflow.com/questions/47973157/replay-series-of-events-with-timestamps-using-rxjs.