Rex sleep

```Rex.sleep``` is so much neater than ```select(nil,nil,nil```. By replacing this we can also easily change the sleeping mechanism in future in just one place...

```
grep -rl "select(nil,nil,nil," . | xargs sed -i 's/select(nil,nil,nil,/Rex.sleep(/g'
grep -rl "select(nil, nil, nil," . | xargs sed -i 's/select(nil, nil, nil, /Rex.sleep(/g'
grep -rl "::IO.Rex.sleep" . | xargs sed -i 's/::IO.Rex.sleep(/Rex.sleep(/g' 
grep -rl "Kernel.Rex.sleep" . | xargs sed -i 's/Kernel.Rex.sleep(/Rex.sleep(/g'
```