Log owner of current tty
set tty_uid to -1 by default, so that tty_uid:0 is always meaningful
Merge remote-tracking branch 'github-tmalkowski/tty_uid'

Also: reworked contributed code as standalone input provider tty_uid.

Conflicts:
	snoopy.c
Removed obsolete configure option --enable-cwd-logging. Superseeded by --with-message-format
Updated readme: added info about developing new input providers