Extract check-style module.

Also fix any checkstyle warnings and errors that were raised.

Fixes #2
Update dependency versions to the latest.

This updates junit, mockito and guava.

Fixes #3
Merge pull request #8 from PressAssociation/update-guava-version

Update dependency versions to the latest.
Merge pull request #7 from PressAssociation/extract-checkstyle

Extract check-style module.
Update the javadoc throughout the project.