New make target for Windows platform: make dist (bug#6602)

New make target for Windows platform: make dist (bug#6602)
* admin/admin.el: Write version number to nt/makefile.w32-in.
* admin/nt/makedist.bat: Remove; replaced with `zipdist.bat'
  in the nt/ directory.
* admin/nt/README.W32: Relocate to nt/ directory.
* etc/NEWS: Document new --distfiles configure.bat option and
  `dist' make target on Windows.
* nt/INSTALL: Document new dist target and add section about
  creating binary distributions.
* nt/configure.bat: New parameter `--distfiles'.
* nt/makefile.w32-in: Add version number, new target `dist'.
  Add new target `install-shortcuts'.
* nt/zipdist.bat: New file; create zipped binary distribution,
  replaces admin/nt/makedist.bat.