Take prj file and create links to Doxygen docu

Created by: chleh

The main part is the script scripts/doc/linked-xml-file.py. The rest is Doxygen docu fixes, and documentation script improvements.

The result of the script looks as follows:

The blue tags are links to the respecitive documentation pages. The red text marks tags whose documentation pages could not be found by the script.

This PR is meant to provide a more intuitive entry point to the project file documentation.