Fix typographic bugs in Logic manual.

Thanks to Rob Arthan for the bug report. Closes #208.

consistent punctuation in enumeration list

extra space (which caused a newline) removed

double 'the' removed

Use the \HOL macro in manuals' section headers now it looks OK.

Remove an unnecessary hyphen in an occurrence of HOL-4

there are four axioms, not five (update to Logic manual)

Have "modernised" the manuals.

1. By default it now uses pdflatex. Postscript can still be generated
with "make ps".

* Authors should not use pstricks - it doesn't work with pdflatex.
* The commuting diagrams in the tutorial have been redone with
XP-pic -- with much less code.
* Other figures can be included with "\includegraphics", which is provided
by the graphicx package. Just make sure you upload EPS and PDF versions
of the diagrams.
* The Covers directory and old logos have been removed -- they weren't
maintainable. (Have tarted up the title.tex pages.)

2. The make files have been updated and cleaned up. There is
now "make clean" option in $HOLDIR/Manuals.

* As a side note, I noticed that a call to "make" in $HOLDIR/Manuals didn't
do anything on Mac OS X. I had to do "make -B".

3. Have eliminated font substitution errors.

* Don't include the charter.sty package - the font is now changed
in LaTeX/layout.sty. This avoids changing the \tt font, which
causes problems with \section{\texttt{stuff}}.
* Left and right braces in \tt font can be a problem. \{ and \} give
maths font, which is fine in places. \verb%{}% will work but
\verb can't be used in certain places (inside another command).
Have added \lb and \rb to LaTeX/commands.tex. These are just
\char'173 and \char'175 and can be used anywhere.

4. Have commented out the mucking about with page numbering.

* This means that if you do a goto page N (in Acrobat, Preview.app etc.)
then you go to page N of the main text. (Stops folks having to add
an offset to entries in the index.)

5. Have made things more compatible with amsmath.

* The environment "boxed" (LaTeX/commands.tex) has been renamed to "holboxed".
* Have changed "\over" to "\frac".
* amsmath is turned on in the Logic manual, mainly to get text subscripts
typesetting better.

6. Have removed a bunch of hbox (and other) warnings.

* Don't do "\begin{session}\begin{hol}\begin{verbatim}...", do
"\begin{session}\begin{verbatim}..." instead.
* Don't use "\begin{hol}\begin{verbatim}..." is item lists.
Instead just do "\begin{verbatim}".
* Have done some small text edits - hopefully these are okay.
* A few more warnings remain and there's not much that can be done
about underfull vboxes -- short of going with "\raggedbottom".

7. Have made Doc2TeX and reference.tex used fancyvrb, This means the
font size can be set to \small globally. Have also removed the
\samepage directive -- a few bad breaks are better than having
material bigger than the size of the page.

A bunch of changing {\small\tt foo} into \ml{foo}.

Extracted chapters one and two from existing DESCRIPTION, and turned them
into a standalone LOGIC manual. Thanks to Mike for the suggestion. Have
yet to adjust the DESCRIPTION. References in LOGIC that used to be sections
using LaTeX \ref, are now typically just to "DESCRIPTION".