Percentage computation rework and more fixes

[stieglma]

• override annotations are now working for supertyes and interfaces (only supertypes before)
• all interesting numbers are added to the report (some were left out before, e.g. enum constants)
• changed htmlexporter a little bit to have a more logical structure
• enum methods values and valueOf were always shown as undocumented although they are predefined and can't even be overridden by the user

Feel free to add comments to the pull request where applicable. I was doing these changes in order to have a better view if my private/publicOnly changes were giving meaningful results.

[stieglma]

Actually I thought a bit more about the logic for counting overridden methods and I think it is still not completely correct: when the super class/interface is not documented, the overriding method is still counted as fully documented. I will add a fix for that on this branch ,too