* 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.
* lisp/org.el (org-git-version): placeholder for recording the Git
version of org during install
* lisp/org.el (org-version): initialize local git-version with
placeholder and fall through using it when org is not installed in
a Git repository
* 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
* Makefile: add an optional include local.mk
* default.mk: install lisp files into org subfolder by default
* lisp/Makefile: new file to handle all make targets within lisp
* lisp/dependencies.mk: dependencies, should rather be auto-generated
* maint.mk: remove obsolete variable definitions
* targets.mk: hand off to sub-make in ./lisp, remove unused targets
