* doc/Makefile: introduce target for git-describe.texi, which is an
automatically generated file that records the output of git-describe
and date; remove this file during make clean
* doc/org.texi: remove @set for VERSION and DATE and do an @include
git-describe.texi instead
* doc/Makefile: cleanall additionally removes the directories for
manual and guide; fix the dir file in infodir after removal of org
documentation
* lisp/Makefile: remove debug statement
* Makefile, lisp/Makefile, doc/Makefile: add target clean-install
to remove files in install-directories
* default.mk: add customization variable $(SED)
* doc/Makefile: do not remove dir while cleaning
* lisp/Makefile: use sed instead of perl to weave git-status into
org.el and ignore any errors while doing it. Keep git status in
$(GITSTATUS) to make it more clear what happens in the check.
* Makefile: use info function for output and call shell only once
* default.mk: add PDFTEX and RMR variables for customization
* lisp/Makefile: add target 'all' and create $(lispdir) if necessary
* maint-targets.mk: invoke sub-make for HTML manuals
* maint.mk: remove unsused VARIABLES
* targets.mk: invoke sub-make for ./doc and clean up some targets
