* docs/Makefile.am (htmlrefpub): Remove override and use the
updated mm-common default value.
* docs/reference/glibmm_header.html_fragment: Adjust links to
the main page and the gtkmm book.
* {glib,gio}/{glib,gio}mm{,-uninstalled}.pc.in (htmlrefpub):
Adjust variable values.
* configure.ac (MM_PREREQ): Require mm-common 0.6.1.