coverage: use lcov to generate coverate reports

Type "make coverage" to generate a coverage report and launch it using
firefox.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter: move LogFilterPipe to a separate module

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-op: split off or/and operations from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-cmp: split off from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-tags: split off from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-netmask: split off from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-call: split off from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-re: split off from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
filter/filter-pri: split off from filter-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
lib/filter: clean up includes

All files should include only the headers required to that specific code.
Since the filter-expr.c file was split, a number of unneeded includes
remained in filter-expr.{c,h}, remove those and make sure the split off files
include what those need.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
test_filters: move from tests/unit to lib/filter/tests

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
rewrite/rewrite-set-tag: split off from rewrite-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
rewrite/rewrite-set: split off from rewrite-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
rewrite/rewrite-subst: split off from rewrite-expr

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
rewrite: clean up includes

Because of the split a number of includes remained lingering, clean them
up.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
lib/filter/tests: preload the syslogformat module

When linking the filter test program, preload the syslogformat module,
so that make check will work without installing syslog-ng.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>