Assume any module with at least one import or export (including export {}) is a module.

Ignore any module failing this.

Keep import/ignore for things like ignoring CoffeeScript, but it will be empty by default. Files matching ignore patterns will be completely ignored, as if they were core modules or CJS.

Technically, this is how ignored files work today; if exports are detected, they are parsed anyway. This reversal makes more sense.

Supersedes: #268
Idea thanks to: #384