Log Message:
Changes 2.26.0:
* Minor documentation build fixes.
* Change public documentation location to library.gnome.org in
  the pkg-config files as well.
* Change public documentation location to library.gnome.org.
* Reenable the per-class hierarchy graphs in the reference documentation.
* Drop the custom HTML header and footer, and use the shared doxygen.css
  file from mm-common.
* More...