Merge branch 'unix-tcp-nodelay' of https://github.com/rraptorr/nghttp2 into rraptorr-unix-tcp-nodelay

This silences warning log that otherwise spams logs on every accepted
connection.

The control process handles signals, reads configuration, reads
private keys, and bind port (which may be privileged one).  It never
drop privileges, so that it can execute new binary with the same
privilege.  It forks worker process.  The worker process handles all
incoming connections.  It drops privilege.

Fixes GH-352