Implement #18 Same source and destination file

This adds support for using the original file as the destination by adding an <!-- /include --> comment as suggested in issue #18.

I also added a `grunt lineendings` task because on my machine when I first cloned the repo two of the tests didn't run as the \r\n and just \n line endings of the source and expectation files didn't match. I didn't commit after running it though to avoid making the diff unreadable.