Add placeholder VERSION.tex and CITATION.bib files

This commit adds templates for VERSION.tex and CITATION.bib: those
files are automatically generated by the makefile to contain the
date and version of the current commit.  Unfortunately, this means
that they do not exist when the repository is first cloned, which
causes errors in LaTeX.  So this commit adds files that explain
that they are just placeholders and gives directions for how to
determine the correct information.  I've also added those directions
to the README file.
Add macro to automate BibTeX typesetting
Add 'http' prefix back to the GNU FDL homepage

Some pdf readers (i.e. Konqueror) wouldn't follow the link
to the GNU homepage without an 'http://' prefix.
Move FDL and author list into the individual pdf files

In earlier versions, we viewed the collection of pdfs as a single
entity and encouraged the FDL and author lists to be distributed
as separate pdf files (to minimize space and duplication).  But
it does seem likely that people will encounter these pdfs separately,
so we've decided to include the license and author list in every
pdf by default.

I still think that our earlier view is correct and that the license
and author list can be distributed once (for example, if the book
is used for a class, the instructor can compile the pdfs without
licensing information, but just give the license to the students
the first day), so this is just a matter of emphasis.