Convert old changelog files from straight up .html to .h files that will be parsed by doxygen.

This will make all changelog files behave the same way.
Merge pull request #21 from bangerth/convert-changelogs

Integrate old changelog files into doxygen

Convert old changelog files from straight up .html to .h files that
will be parsed by doxygen. This will make all changelog files behave
the same way.