Created by: donaldpipowitch
I don't know if this pull request is welcome, but I've refactored and renamed some grid mixins.
I think they are more descriptive (e.g. .loop-grid-columns is much clearer as .make-grid in my opinion). And I also DRY'ed up the generation of screen size dependend grids (xs, sm, md, lg) with a new mixin.