doc: Use Makefile rules to auto-generate EDITION Texinfo variable for octave.texi * octave.texi: Use @include to include new "octave-doc-version.texi" file with EDITION variable. Use @value{EDITION} in @subtitle macro to avoid having to manually change text for every release. * doc/interpreter/module.mk: New rule to build "octave-doc-version.texi" which depends on "version-octave.texi" that is created by Automake. Change documentation target rules for .info, .dvi, .pdf, .html to depend on "octave-doc-version.texi". Add new file to doc_EXTRA_DIST and doc_MAINTAINERCLEANFILES to distribute it in tarball and to clean it up.