[syslog-ng] [PATCH (3.5) 0/6]: Type hinting support

[Gergely Nagy]

The following patchset introduces type hinting support, for mongodb
and format-json for the time being, along with a couple of cleanups
done prior to the introduction.

The code passes unit and func tests, and is the result of a pair
programming session by Balazs Scheidler <bazsi at balabit.hu> and myself,
I rearranged the result and split it up into individual, mostly
self-contained commits.

To use type hinting with value-pairs:
 value-pair(pair("SOME-INTEGER" int("1234"))
            pair("SOME-DATETIME" datetime("$UNIXTIME")));

Simiarly, with format-json:
 template("$(format-json some-integer=int(1234) some-datetime=datetime($UNIXTIME))\n")

Further documentation will follow later, most likely in a form of a
blog post.