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.

2006/toledo2/README.md

@@ -118,9 +118,9 @@ each line:
     RUN
 
     10 FOR A=1 TO 10
-    20 PRINT A\
-    30 NEXT A\
-    LIST\
+    20 PRINT A
+    30 NEXT A
+    LIST
     RUN
 
     10 INPUT A

2006/toledo2/index.html

@@ -218,9 +218,9 @@ each line:</p>
     RUN
 
     10 FOR A=1 TO 10
-    20 PRINT A\
-    30 NEXT A\
-    LIST\
+    20 PRINT A
+    30 NEXT A
+    LIST
     RUN
 
     10 INPUT A