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.

2011/toledo/README.md

@@ -110,9 +110,9 @@ extra points.
 
 
 Caveat: You can shoot only 3 bullets at a time.
-\
+
 Trick: You can fire faster if they explode on anything.
-\
+
 Believe it or not, it has strategy!
 
 When only one tank remains on the field, the level will advance.

2011/toledo/index.html

@@ -214,9 +214,9 @@ blue when the view goes inactive.</p>
 <p>The objective is to chase and destroy the other player’s tank.
 There is also an aqua tank for testing your aim and getting
 extra points.</p>
-<p>Caveat: You can shoot only 3 bullets at a time.<br />
-Trick: You can fire faster if they explode on anything.<br />
-Believe it or not, it has strategy!</p>
+<p>Caveat: You can shoot only 3 bullets at a time.</p>
+<p>Trick: You can fire faster if they explode on anything.</p>
+<p>Believe it or not, it has strategy!</p>
 <p>When only one tank remains on the field, the level will advance.
 Don’t forget to destroy the aqua tank.</p>
 <p>The <strike>battle</strike>playground is surrounded by mountains and each level is