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.

1991/rince/README.md

@@ -87,15 +87,15 @@ Key to map:
      ######                 | | | /\   /--\  ==|    /\ | |  Directonal keys
      ######  Solid Wall     | ----||    \/     /\   ||----  (unlock doors of
      ######                 |     \/  ==|     \--/  \/       the same direction)
-			    |\
+			    |
 			    |   <<                    >>    Doors. Unlocked by
 	     Blank space    |   <<   vvvvvv  ^^^^^^   >>    the above keys.
 			    |   <<                    >>
-			    |\
+			    |
        ___                  | o__O\   O__O   ^__^   /O__o\
       /   \  'Crushable'    | \___/  /----\ /----\  \___/  The four sprites for
       \___/    boulder      |  _/_\  _/  \_ _/  \_  /_\_   your character :-)
-			    |\
+			    |
        ___   uncrushable    |   /\   Diamonds. They can either be found lying
       /@@@\    boulder      |  <  >  around (if only!) or manufacture by pushing
       \@@@/                 |   \/   two 'crushable' rocks together.