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`.

1989/fubar/README.md

@@ -26,7 +26,7 @@ For more detailed information see [1989 fubar bugs](../../bugs.html#1989_fubar).
 ## Try:
 
 ```sh
-./try.sh # run on 1 - 7 
+./try.sh # run on 1 - 7
 
 ./fubar.sh 2 # run via script
 ./fubar 2 # run directly