add new detector which uses Guava's @VisibleForTesting.
close #22: detect FindBugs warning which has no justification.
improve error handling: notice which class has problem clearly
Merge remote-tracking branch 'worksap/master' into visible-for-testing

Conflicts:
	README.md
Merge pull request #23 from KengoTODA/visible-for-testing

Introducing 2 new detectors which checks annotation