Option to output results to file

Since I needed this option for the app I created for the ClojureCup ([Good, Bad. Ugly](https://clojurecup.com/?#/apps/goodbadugly)) this year, I forked the Eastwood repository and added this very simple feature. The output that was sent to `stdout` wasn't quite what I needed since it has some other information which made the results hard to parse. I found this useful and the implementation simple so I thought about sharing. Please let me know what you think.