Add health check

[jpneverwas]

Hi,

I've also experienced a bit of downtime (likely) related to #21. The rather effective caveman workaround I've resorted to may be too crude for anyone's liking, so I present it here with all humility. Basically, this provides a tiny second binary to be built and included alongside the main one. Docker automatically uses this to gauge the health of the main process. Those not using capital "D" docker can either exec the command manually or hit an included HTTP endpoint that provides similar utility.

This all works in the dumbest way possible: by having an incoming PONG handler print a timestamp to a file whenever it runs, thereby providing an out-of-band heartbeat for any external monitor/supervisor to look for (two periods elapsing without an update means it's time to restart the daemon). This has saved me multiple times, but I completely understand if people find it too simplistic or just gross.

Thanks.

[russss]

I think I'm going to leave this one unmerged for the moment, but I should really try and work out why this failure is happening. (It does happen on my irccat instances, but only once every 6 months or so, so it's a bit of a pain to debug.)

Thanks for all your PRs and sorry for the slowness in getting them merged!

[jpneverwas]

Not at all. Happy to contribute.

[cmsj]

@russss if it helps, I run irccat on a home server and I reliably get the "it's running, but nothing is happening" issue every time my home internet connection drops and reconnects. Might make it easier to reproduce?