Fix many javadoc errors and warnings
Updated plugin versions referenced in pom.xml
Merge pull request #154 from sharwell/updates-for-release

Updates for release
[maven-release-plugin] prepare release 3.5.2
[maven-release-plugin] prepare for next development iteration
Merge pull request #155 from sharwell/release/3.5.2

Release/3.5.2
Update CHANGES.txt