Citations of third-party works in appendix only.

As alluded to in 2ea19b71d4a917babb29024f06acabfe73309f40 's commit
message on 2014-12-17 19:52:15 -0500, keeping any information on a
part-by-part basis is difficult and error-prone, since there exists no
reliable way to auto-generate such information accurately.

Therefore, citations to third-party works, in addition to remaining
fully documented in the commit log as they always have been, are now
placed in specifically one location in the body of the text itself: a
single appendix specifically designed for that purpose.

In this manner, contributors have no house-keeping work regarding
citations. Contributors need only list third party works and links in
one place: third-party-citations.tex.

Documentation in CONTRIBUTING.md for making contributions of third-party
works is left as a TODO.

Hack to get all menus to appear in right places.

The only way I could figure out how to get different output for
monolithic and section-based versions was to do this rather odd hack,
which uses tex4ht.usr to conditionally insert specific bootstrap HTML
for the mention that will allow proper formatting.

Prefer footnotes at bottom of each page.

Without "fn-in" option, the footnotes each get their own page, which
seems silly.

This fixes that.

Also included are more rm files, so htlatex doesn't freak when it gets
run again after html files have been moved to public_html.

BOOK_CLASS_FILE is not used.

It was a vestige from old Makefile.

Hack tex4ht's overlib stuff to use jQuery tooltip

tex4ht supports "overlib" for footnote popups. The hack is pretty
straightforward; it dumps a Javascript area into a .js file that can
then be used by overlib to popup stuff.

This hack is to use that output to make the same thing work with jQuery
UI's tooltip widget.

Note that we run with overlib support first, then *without* it in the
Makefile setup. This is to force the needed .js file to be generated,
but make sure the HTML doesn't try to load overlib (which is default).

(This should be adapted as a patch to upstream tex4ht ultimately.)

Also included herein are improvements to the Makefile to build the HTML
output.