Coverage: Fixed sonar findings in 0.3.0 (#33)

* #12: Prepared signing.

* #12: Updated version number to 0.3.0

* #12: Removed GPG signing execution.

* #12: Removed Travis CI run with Java 11 because of JavaDoc incompatibilities (see #19).

* Update README.md

* Update README.md

* #23: Added Sonar checks and badges. (#26)

* #23: Added Sonar checks and badges.
* #23: Updated Surefire plugin version to 3.0.0-M3.
* #23: Added Jacoco plugin.

* #12: Added support for value tables. Adapted dependent code. (#22)

* #12: Added support for value tables.

* #27: Fixed Sonar findings. (#28)

* #27: Fixed Sonar findings on 0.3.0.