Fix Doxygen warnings

[ischoegl]

Changes proposed in this pull request

Fix remaining Doxygen warnings (doxygen=1.9.2), plus address several broken links.

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] Build passes (scons build & scons test) and unit tests address code coverage
• [x] Style & formatting of contributed code follows contributing guidelines
• [x] The pull request is ready for review

[ischoegl]

Addressed (and rebased)