doc directory Makefile commands

The following Makefile commands may be issed while the doc directory is the current directory:

• make doc | make doc.all
  Will run Latex on the VMD documentation files, and produce all the guides for VMD. The following documents will be produced:
  1. ig.dvi the VMD Installation Guide.
  2. pg.dvi the VMD Programmers Guide.
  3. ug.dvi the VMD Users Guide.
• make doc.[ig | pg | ug]
  Will run Latex and create the specified guide document, i.e., the VMD Users Guide if make doc.ug is entered.
• make doc.book
  This will format all the VMD documentation guides into a single document in book format, with each individual Guide in a separate Part. The resulting file will be called vmd.dvi.