fix problematic HTML caused by certain trailing backslashes

In cases that are **outside of a markdown code block**,
a markdown line with ending in a tailing "\" can generate
problematic HTML.

We certain trailing backslashes outside of a markdown code block
with "<br>" HTML elements, or in some cases eliminated the
need for a trailing backslash.

In a few cases some unnecessary trailing backslashes inside
of a markdown code block were removed.

The following markdown files were changed in this commit:

```
1990/dds/README.md
1990/jaw/README.md
1991/ant/README.md
1991/rince/README.md
1991/westley/README.md
1992/vern/README.md
1992/westley/README.md
1998/schweikh1/README.md
2004/anonymous/README.md
2005/sykes/README.md
2006/toledo2/README.md
2011/toledo/README.md
2012/endoh2/README.md
2012/tromp/README.md
2013/robison/README.md
2015/hou/README.md
2015/howe/README.md
2015/schweikhardt/README.md
2018/burton1/README.md
2018/burton2/README.md
2018/ferguson/README.md
2018/vokes/README.md
2020/ferguson1/README.md
```

Performed `make www` to test these changes.

1998/schweikh1/README.md

@@ -171,7 +171,7 @@ C compilers.
 
    is rejected by tcc version 4.1.2, the TenDRA compiler:
    ```
-   "t.c", line 3: Error:\
+   "t.c", line 3: Error:<br>
    [ISO 6.8.3.3]: Invalid result for '##' operator in macro 'H'.
    ```
 

1998/schweikh1/index.html

@@ -261,7 +261,7 @@ at least one compiler falls over.</p>
 <pre><code>    #define H(x) &lt;st##x##.h&gt;
     #include H(dio)              /* expands to &lt;stdio.h&gt; */</code></pre>
 <p>is rejected by tcc version 4.1.2, the TenDRA compiler:
-<code>"t.c", line 3: Error:\    [ISO 6.8.3.3]: Invalid result for '##' operator in macro 'H'.</code></p>
+<code>"t.c", line 3: Error:&lt;br&gt;    [ISO 6.8.3.3]: Invalid result for '##' operator in macro 'H'.</code></p>
 <p>To be honest, I don’t know if the rules for pp-tokens and token
 pasting don’t forbid what I do (and thus tcc is correct in rejecting it).
 In this case, all other compilers I tried are buggy, or the Standard