* .gitignore: change as in <URL:https://live.gnome.org/
	GnomeGoals/NewDocumentationInfrastructure>
	* Makefile.am: ditto.
	* autogen.sh: remove gnome-doc-tool code.
	* bootstrap.sh: ditto.
	* configure.ac: test `which yelp-build` to detect yelp-tools
	package, warn if not found, but continue to configure with
	documentation disabled.