Man, this is really sexy! :)
So sexy that one hesitates to make additional suggestions. So ignore this: in my window-proportions (retina 15') the code preview feels a little bit too small. I am tempted to drag the separation line between entry-list and preview up a little and find it's not possible.
Being able to open the file in a split (I won't be as bold as to ask for a new editor window ;) ) would be very nice too (maybe right-click or context menu).

Can we merge? You've seen my layout changes in the other branch, which I think address what you mentioned, but I'd rather get feedback from more users before further fiddling.

Sure to both ;)