Cleanup

- Rename and move the variable to variables file
- Move code to the grid file
- Use the mixin to generate our own classes
- Wrap in a grid classes enabled conditional
- Document the mixin

scss/_grid.scss

@@ -46,6 +46,16 @@
     @include make-row();
   }
 
+  @each $breakpoint in map-keys($grid-breakpoints) {
+    $infix: breakpoint-infix($breakpoint, $grid-breakpoints);
+
+    @for $i from 1 through $grid-row-columns {
+      .row-cols#{$infix}-#{$i} {
+        @include row-cols($i);
+      }
+    }
+  }
+
   // Remove the negative margin from default .row, then the horizontal padding
   // from all immediate children columns (to prevent runaway style inheritance).
   .no-gutters {