[WIP] Update Doxygen documentation for MarlinReco packages

[dudarboh]

BEGINRELEASENOTES

• Add paths of all MarlinReco processors to the INPUT of doxygen
• Enable source browser and modify few style settings to match ROOT format
• Document existing processors into separate categories
• Minor clean up of documentation

ENDRELEASENOTES

TODO:

• [ ] Create subgroups of documentation for separate processors
• [ ] Add existing README subpages into documentation
• [ ] Remove documentation of empty namespaces, etc

[dudarboh]

Hi @tmadlener,

At this point I would consider this a basic minimal PR. It just adds paths of processors for documentation.

But as you can see from TODO list, there still few things I would like to add, to make it look fancier than just a list of classes. But these would require a bit more changes in many files, so just in case if you won't be happy with those changes we can always come back to this commit in the end.

[tmadlener]

Thanks @dudarboh. I have no particularly strong feelings about the style or the overall organization. I just saw that you have tweaked quite a few doxygen defaults. Do you happen to have the current results of running doxygen on MarlinReco available somewhere? I think it might be easier to look at the result, rather than sifting through doxygen configuration and guessing what it might look like in the end. There was a link in #104 somewhere, is that pointing to the current version? (Doesn't really matter if that PR is part of the output).

[dudarboh]

@tmadlener For debugging purposes, I will host documentation from current PR here: https://www.desy.de/~dudarboh/marlinreco_doc/html/index.html