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`.

2012/deckmyn/deckmyn.md

@@ -1,4 +1,4 @@
-# USER MANUAL 
+# USER MANUAL
 
 
 ## Calling the program