Fix code blocks in 1991 and part of 1992

In 1991 the code blocks in the html files should look better with
smaller screens.  In one entry, rince, an image was added as the
formatting is too complicated to get right. The text was changed from
two columns to one column and then a screenshot was taken so that it's a
bit easier to see with smaller widths. This looks fairly good on mobile
phones too. The only downside, of course, is if the web pages ever
change to have a different background or code colour it won't match but
it did not look right with mobile phones. This required a manifest
update.

In 1992 one entry's html file defeated me for now so I had to stop. This
can be looked at later. The last entry I am committing changes to is
1991/buzzard.1. It was buzzard.2/buzzard.2.design.md that is a big
problem and will have to be done another time.

1991/dds/README.md

@@ -53,7 +53,7 @@ of the DDS-BASIC interpreter.  The program needs an executable C compiler called
 ### Program commands:
 
 
-- variable names `A` to `Z`
+- variable names A to Z
 - FOR var = exp TO exp
 - GOSUB exp
 - GOTO exp

1991/dds/index.html

@@ -427,7 +427,7 @@ of the DDS-BASIC interpreter. The program needs an executable C compiler called
 <code>cc</code> in your path in order to work.</p>
 <h3 id="program-commands">Program commands:</h3>
 <ul>
-<li>variable names <code>A</code> to <code>Z</code></li>
+<li>variable names A to Z</li>
 <li>FOR var = exp TO exp</li>
 <li>GOSUB exp</li>
 <li>GOTO exp</li>