fanotify.7, fanotify_init.2, fanotify_mark.2: Document FAN_REPORT_FID and directory...

fanotify.7, fanotify_init.2, fanotify_mark.2: Document FAN_REPORT_FID and directory modification events

Details relating to the new initialization flag FAN_REPORT_FID has been
added. As part of the FAN_REPORT_FID feature, a new set of event masks are
available and have been documented accordingly.

A simple example program has been added to also support the understanding
and use of FAN_REPORT_FID and directory modification events.

Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>