remove all trailing blank lines and all trailing whitespace

Remove all the trailing whitespace:
```
find * -type f -exec sed -i -E 's/[[:space:]]*$//' {} \;
```

Remove the last trailing blank line (might need to be run several times for maximum efficiency - or you just manually handle the changed files `git diff` shows you after the first run):
```
for file in $(find * -type f -exec sh -c '[ -z "$(sed -n "\$p" $1)" ] && echo "$1"' _ {} \;); do
head --lines=-1 ${file} | sponge ${file};
done
```
Warning: This is not space-in-filename friendly. Use `-print0` and `"` to resolve if needed. RIOT doesn't have files with spaces luckily)

`sponge` is part of the brilliant `moreutils` package btw.

Warning: Use these with care if you have binaries lying around .. `git clean -n -x -d -f` is your friend.