new flex-omega mixin

flex-omega.scss

@@ -0,0 +1,58 @@
+@charset "UTF-8";
+/// Creates a margin right on the last object in the row and the last 
+/// object in the container which causes a centered flexbox to self correct.
+///
+/// It also brings back the neat 1.8 behavior of clearing *n + 1 block element,
+/// which addresses a secondary edge case where short elements don't
+/// clear the full row in floated 'box' layouts.
+///
+/// @group Features
+///
+/// @name Flex-omega
+///
+/// @argument {number (`nth-of-type`) | auto} [auto]
+///   When passed an `nth-of-type` argument of type `*n` with `block` display, 
+///   the flex-omega mixin automatically creates a margin right on the last 
+///   object in the row and the last object in the container,
+///   which causes a centered flexbox to self correct.
+///   Note that this mixin does NOT clear floats in order to allow for complex nth selectors.
+///
+/// @argument {map} $grid [$neat-grid]
+///   The grid to be used to generate the margins.
+///   By default, the global `$neat-grid` will be used.
+///
+/// @example scss - Usage
+///   .element {
+///     @include flex-omega;
+///   }
+///
+///   .nth-element {
+///     @include flex-omega(4n+1);
+///   }
+///
+/// @example css - CSS Output
+///   .element:last-child {
+///     margin-right: 20px;
+///   }
+///
+///  .nth-element:last-child {
+///     margin-right: 20px;
+///   }
+///
+///   .nth-element:nth-of-type(4n+1) {
+///     margin-right: 20px;
+///   }
+
+@mixin omega($selector: auto, $grid: $neat-grid) {
+  $_grid-gutter: _retrieve-neat-setting($grid, gutter);
+
+  &:last-child {
+    margin-#{_neat-opposite-direction($grid)}: $_grid-gutter;
+  }
+
+  @if $selector != auto {
+    &:nth-of-type(#{$selector}) {
+      margin-#{_neat-opposite-direction($grid)}: $_grid-gutter;
+    }
+  }
+}