Initial version of grok support
grok: Add README
grok: Fixed grok grammar file.
grok: Added test stub
grok: Added first unit test
grok: Refactored testcase, added grok debug option.
grok: Further improvements.

pattern_directory() works now, pattern() renamed to match(),
added tagging, but it doesn't work yet.
grok: Finished grok parser
grok: Updated README
grok: Added extra check for pkg-config.
grok: Added example configuration
grok: Makefile fixes.
grok: Made grok 3.6 compatible and eliminated some warnings

Also added libgrok-dev dependency for travis build.
Merge pull request #90 from talien/feature/grok

Feature/grok