This provides a module to produce logs on an Apache Kafka
distributed queue.

The configuration allows choosing a fixed, random or dynamic
partition key for payloads. Message payloads are generated
with a template. The configuration also allows setting
arbitrary metadata and topic metadata.
modules: Do not count inserted/sent messages as stored ones.

Stored messages are for only queued messages inside syslog-ng.
configure: Reworked common cflags and lib variables for incubator.

Introduced INCUBATOR_LIBS and INCUBATOR_CFLAGS make variables to be able to
link modules more easily, and added convenient INCUBATOR_TEST_LDADD
variable for unit test linking.
ZMQ: Added zmq source, destination and transport
ZMQ: Make useage of zmq automatic

 * It means if user didn't set --enable-zmq,
   but zmq is installed it will compile with zmq
ZMQ: removed unused zmq_install.sh

 * It doesn't belong to incubator. It needed for travis only.
ZMQ: fixed zmq libs and cflags
ZMQ: Fixed segfault during reader deinit