Remove float from .column on screens <=640px

It doesn't make much difference since it has `width: 100%;`, but I needed `<hr>` between columns on <=640px screens, and that `<hr>` is visible only on those screens, removing float allowed me to use margins correctly on `<hr>` element to set some spacing between elements.
Merge pull request #1 from Gavrisimo/patch-1

Remove float from .column on screens <=640px