Add support for logic operator regarding responsive columns

[JorgeSivil]

Right now the only possible usage is X < Y, while in my project, we use mobile as default, tablet-up, and desktop-up breakpoints.

Having this library in the contrary ways makes me test all manually.

So it would be nice to allow the operator, i.e. instead of hardcoded <, maybe allow for the operator definition? Lilke

{ '>= 1000px': 2 }

Or something like that.