configure.ac: Add support for --enable-debug

This adds an --enable-debug option which turns on the ENABLE_DEBUG macro
if passed to configure. It does not touch the CFLAGS, as we should be
building with -Wall -g anyway, and the level of debugging info needed is
best left for the user. This closes #76.

Reported-by: Viktor Tusa <tusavik@gmail.com>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #78 from algernon/f/configure/enable-debug

configure.ac: Add support for --enable-debug
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.
Merge pull request #77 from balabit/feature/kafka

This provides a module to produce logs on an Apache Kafka
modules: Do not count inserted/sent messages as stored ones.

Stored messages are for only queued messages inside syslog-ng.
Merge pull request #79 from talien/f/do-not-count-inserted-messages-as-stored

modules: Do not count inserted/sent messages as stored ones.
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.
Merge pull request #86 from talien/f/make-variables-rework

configure: Reworked common cflags and lib variables for incubator.
Updated README
Initial version of grok support
grok: Add README
grok: Fixed grok grammar file.
grok: Added test stub
grok: Added first unit test