Fundamentally on Flake8 2.x using -q altered the format of the errors
(and the behaviour a little) so it makes the most sense to implement
this logic with formatters rather than messy logic spread throughout
the project.

The FilenameOnly formatter will keep track of filenames already reported
and only print the name once while Nothing will print nothing.

Closes #180

I'm not sure where this code went or when, but it disappeared. Let's
add it back.

Related #180

Some plugins (e.g., flake8-future-import) report errors for empty
files. Those plugins default to reporting the line number as 1 which
caused earlier versions of Flake8 3.0 beta to crash on an IndexError

Closes #157

This is an emerging best practice and there is little reason to not
follow it