remove trailing blanks in markdown files

We used this command to find markdown files with trailing whitespace.

```sh
find . -name '*.md' -print0 | xargs -0 grep -E -l '[[:space:]][[:space:]]*$'
```

After removal, we did a `make www`.

1992/buzzard.2/buzzard.2.design.html

@@ -311,7 +311,7 @@ entirely different subject.)</p>
 
 test
 
-( The result of running this program should be: 
+( The result of running this program should be:
 Hello
 )</code></pre>
 <h2 id="section-2-motivating-third">Section 2: Motivating THIRD</h2>
@@ -711,7 +711,7 @@ scan the input until it finds a <code>)</code>, and exit.</p>
 : &lt;= 1 + &lt; ;
 : &gt;= swap &lt;= ;
 
-: inci 
+: inci
   r @ 1 -   ( get the pointer to i )
   inc       ( add one to it )
   r @ 1 - @     ( find the value again )
@@ -810,7 +810,7 @@ fix-::
 : dump _dump ;
 
 : # . cr ;
-  
+
 : var &lt;build , does&gt; ;
 : constant &lt;build , does&gt; @ ;
 : array &lt;build allot does&gt; + ;