json, state: Added json-c as a git submodule.
state: Added StateHandler framework

StateHandler framework simplifies the usage of persist file entries.
It has a simple interface and it can contain several typed name-value
pairs. This patch does not contain the follow-up of this patch in the
other part of the syslog-ng.
rcptid: WIP: Added unique receipient id feature.

This id is persistent across restarts.

Config option is not implemented yet.
serialization: Added logmsg and nvtable serialization.

Added large number of tests for deserialization, especially for older
types of serialized log messages.