Use "flag" for command line arguments

Using the flag package allows for easy command-line flags (!!!). As an example, I added some for the console, which for regular usage would be quite a pain to have hanging around. Of course, this should be toggleable from inside the application, but this is a start.

It also allows easy "proper" handling of file names. Right now, any non-flag is a filename, and causes a view to be opened, just like other terminal editors do.