Use Merge/Diff Interface when autoformatting

"Auto-correct" now brings up the Merge/Diff panel, as talked about in #10 and #1...

![screenshot 2015-01-01 15 31 45](https://cloud.githubusercontent.com/assets/314997/5591858/210445b2-91cf-11e4-9670-1d6ec180a83f.png)

![auto-correct-merging](https://cloud.githubusercontent.com/assets/314997/5591854/7687dd06-91ce-11e4-8e0a-8382a8ba8554.gif)

What do you feel about this workflow? I think it's more powerful, but perhaps less simple than in #10?