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`.

1993/rince/design.md

@@ -11,9 +11,9 @@ A standard automata would have 2 rules something like this:
 
 ```
 
-		o..			...	  
-		\..  -->  'o'		.o.  -->  '.'    
-		...			.\.   
+		o..			...
+		\..  -->  'o'		.o.  -->  '.'
+		...			.\.
 ```
 
 However, the system I devised, in order to keep things small and neat(!),