Support windows line endings on non-windows platform

For better or for worse, we have a project that uses windows line endings, which is used on both OSX and Linux. `yapf` does not appear to have any knobs to control line endings, instead using the line endings of the platform on which it is run, meaning that a run of `yapf` changes every single line even if there are no real changes to the formatting. Since we use `hg` which doesn't appear to have as good line ending support as `git`, it would be great if there were an option to tell `yapf` which line ending to use.