There's no longer any reason to come out of sleep for periodic service
which has been eliminated by lws_sul.
With event libs, there is no opportunity to do it anyway since their
event loop is atomic and makes callbacks and sleeps until it is stopped.
But some users are relying on the old poll() service loop as
glue that's difficult to replace. So for now help that happen by
accepting the timeout_ms of -1 as meaning sample poll and service
what's there without any wait.
https://libwebsockets.org/pipermail/libwebsockets/2019-April/007937.html
thanks to Bruce Perens for noting it.
This doesn't change the intention or status of the CC0 files, they were
pure CC0 before (ie, public domain) and they are pure CC0 now. It just
gets rid of the (C) part at the top of the dedication which may be read
to be a bit contradictory since the purpose is to make it public domain.