Add long overdue README

Includes a statement of purpose, a brief configuration guide, and
protocol documentation intended to be used by implementors of
pg_logfebe servers.
Rope in my fine colleagues at security@ in case of my absence
Do not retry close() on EINTR

This would represent file descriptor corruption in a multi-threaded
program (since the file descriptor number could be reused), but as
Postgres has no such execution such a loop seems harmless for now: the
second loop after EINTR would result in a prectable EBADF and then
subsequently exit.
Merge remote-tracking branch 'github/master'
Non-PGXS-compatible Makefile