eventlog: new package

eventlog is a library for creating structured events from
applications, and is the workhorse behind syslog-ng's own messages.

[Thomas:
 - fix alphabetic ordering in package/Config.in, as noticed by
   Vicente.
 - rewrap Config.in help text and add some URL as a reference (though
   the eventlog project doesn't seem to have a real web page)
 - remove useless slash at the end of EVENTLOG_SITE
 - make the license info more specific: it's a BSD-3c license
 - add a hash file.]

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>