add spacing mixins

src/scss/_mixins.scss

@@ -38,6 +38,11 @@
 	@include pb($bottom);
 }
 
+@mixin pad-h($left, $right: $left) {
+	@include pl($left);
+	@include pr($right);
+}
+
 @mixin pad($amount-t, $amount-r: $amount-t, $amount-b: $amount-t, $amount-l: $amount-r) {
 	padding: #{$amount-t * $line-height}rem
 		#{$amount-r * $line-height}rem