Split flexDirection into its own plugin

src/plugins/flexDirection.js

@@ -0,0 +1,21 @@
+export default function({ variants }) {
+  return function({ addUtilities }) {
+    addUtilities(
+      {
+        '.flex-row': {
+          'flex-direction': 'row',
+        },
+        '.flex-row-reverse': {
+          'flex-direction': 'row-reverse',
+        },
+        '.flex-col': {
+          'flex-direction': 'column',
+        },
+        '.flex-col-reverse': {
+          'flex-direction': 'column-reverse',
+        },
+      },
+      variants
+    )
+  }
+}