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`.

2005/anon/README.md

@@ -282,7 +282,7 @@ well. How does it achieve this incredible feat?
 
 ### SPOILER
 
-Read the following only if you give up figuring it out :-) 
+Read the following only if you give up figuring it out :-)
 
 #### The Evil Hack