Request: Done and open next shortcut #69

I would really like to be able to mark the current file as done AND open the next file.

Suggest we use m (Critique's shortcut). Shift-m could go backwards

I would like it to open the next file that has not be reviewed, but I'd also be happy for it to open the next file regardless of review state.

It should NOT toggle the reviewed status, i.e. if I hit this key n times then those n files will end up in a "seen" state always.