Add logical properties

sass/utilities/initial-variables.sass

@@ -75,3 +75,4 @@ $speed: 86ms !default
 // Flags
 
 $variable-columns: true !default
+$rtl: false !default

sass/utilities/mixins.sass

@@ -128,6 +128,26 @@
     @media screen and (min-width: $fullhd)
       @content
 
+=ltr
+  @if not $rtl
+    @content
+
+=rtl
+  @if $rtl
+    @content
+
+=inset-inline-start($spacing)
+  @if $rtl
+    right: $spacing
+  @else
+    left: $spacing
+
+=inset-inline-end($spacing)
+  @if $rtl
+    left: $spacing
+  @else
+    right: $spacing
+
 // Placeholders
 
 =unselectable