Add a helper function to generate decorators for mixin inclusion

lib/mixins/include.js

@@ -0,0 +1,20 @@
+'use babel'
+
+/**
+ * Generates a decorator function to includes many `mixto` mixins into a class.
+ *
+ * @param  {...Mixin} mixins the mixins to include in the class
+ * @return {function(cls:Function):Function} the decorator function that will
+ *                                           include the specified mixins
+ * @example
+ * @include(SomeMixin)
+ * export default class SomeClass {
+ *   // ...
+ * }
+ */
+export default function include (...mixins) {
+  return function performInclusion (cls) {
+    mixins.forEach((mixin) => { mixin.includeInto(cls) })
+    return cls
+  }
+}