Add missing changelog for version 1.1.13.
Merge pull request #500 from bernd/changelog-update-1.1.13

Add missing changelog for version 1.1.13
ruby filter: multi-instance support
Merge pull request #501 from nikicat/fix-ruby-filter

ruby filter: multi-instance support
- try to fix prune specs, but I think there are actually bugs found by
  the tests that need fixing now.
- fix range filter specs
- fix split filter specs
- fix translate filter specs
- default useragent filter to target the root of the event instead of
  writing into the "ua" field.
- fix useragent specs
- fix xml specs
Fix another json spec failure (typo)
- fix alter filter specs
- fix failling clone filter spec (Event#clone wasn't a deep enough copy)