Added some new cruft.

For some of the "big" targets, force things to happen in the "right"
subdirectory, i.e., "make" will build the DVI and PostScript files in the
paper-letter/ directory, and "make PAPER=a4" will build DVI and PostScript
files in the paper-a4/ directory.

Probably still needs some restructuring.

most of the processing is the same and has to be done anyway.

Using \input instead of \include to avoid extra .aux files from being
generated.

Some targets may be a little raw, but the basic formatting targets are all
tested, primarily for use from the subdirs.  There are probably a few
gotchas, and the paper-*/ directories could use "helper" Makefiles.

Most of the logic is still in the primary Makefile and a new script in
Doc/tools/.

enough platforms).

didn't work, because the resource file chain was incomplete when we
tried to open the preference file. Fixed.

api, ext, ref, and tut manuals.  The Library Reference requires too much
special index processing to make it beneficial to extend this to support
it.

Normalize some other markup.

\itemjoin,
\kwindex:  Revived definitions to support the Python Reference Manual.

This is handy for comparing plain-text documentation files,
since it displays intra-line differences.

and the "key" keyword parameter was used to invoke .go(), use the directory
of the selected file as the stored directory to return to when the same key
is used again.  This is useful since the user may well entry at least part
of the path in the filename box instead of doing a lot of clicking around in
the listboxes.