Adds support for automatically keeping you offline at night. I keep wanting to do one more thing, and so find it hard to log off and sleep.
Commands:
/sleeptime clear - Deactivate bedtime enforcement
/sleeptime set <time> - Sets your bedtime.
If you have a bedtime set, you won't be able to log in from your bedtime until 8 hours later. As you approach your bedtime you'll get warnings for 1 hour, 30 minutes, 5 minutes, 1 minute, 30 seconds and 10 seconds, before being logged off. Note that the time is server time, not your local time if that's different!
You can't change your bedtime when it's less then an hour to your bedtime - this also means that if you set your bedtime to less than an hour in the future then you won't be able to change it back or clear it. Be careful!
(Updated for 1.16; for previous versions the command works slightly differently)
