* autogen.sh: Use `gnulib-tool' to install gendocs.sh.
* Makefile.am (web-manual): New target. Builds a web manual using
gendocs.sh.
* configure.ac (AC_PREREQ): Require Autoconf 2.59 or later.
Use more standard `doc' directory.
* docs: Rename to ...
* doc: ... this. Update all users.
* doc/multiboot.texi: Fix an obsolete reference to `docs' directory
in GRUB distribution.