Add an auto-view mode

[cbrown1]

I propose a minor change that allows the user to include a switch at launch, to change behavior so that a markdown file is loaded and displayed when it is selected (no need for the enter key). So if I have a folder full of markdown files, I can scroll over them and each is displayed as it is selected.

With this change, along with the ability to launch an external editor, frogmouth would be a powerful notes app. User could point it to a notes directory, where he could quickly scroll through all notes, and hit enter to load the selected note into his favorite text editor to edit. Folders would be notebooks, and markdown files would be notes, no changes needed there. One additional change would be a function to create a new note, which seems pretty simple to implement. There is no notetaking app that I am aware of that would work as well (or look as good). The idea is that we all have an editor we are comfortable with, so for good note taking what is needed is a solid interface to browse notes and launch the editor when needed. Frogmouth is 95% there as is.