Merge pull request #4 from martin-g/master

Wicket-Bootstrap #280 - Return null if a resource cannot be found
[maven-release-plugin] prepare release wicket-webjars-parent-0.3.3
[maven-release-plugin] prepare for next development iteration
- update wicket 6.12 and webjars-locator 0.6
Update README.md
PR #4 - Log a debug when a resource cannot be found