Watermark filter documentation update. Fixes #404
Merge pull request #406 from me1ifaro/watermark-documentation-fix

Watermark filter documentation update. Fixes #404
[ci] run tests only on 2.3 version.
Merge pull request #407 from formapro-forks/travis-run-only-on-23

[ci] run tests only on 2.3 version.
Merge remote-tracking branch 'upstream/master' into issue-369-fix