Complete builders, start work on using them

src/Discord.Net.Commands/Extensions/IEnumerableExtensions.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+
+namespace Discord.Commands
+{
+    public static class IEnumerableExtensions
+    {
+        public static IEnumerable<TResult> Permutate<TFirst, TSecond, TResult>(
+            this IEnumerable<TFirst> set,
+            IEnumerable<TSecond> others,
+            Func<TFirst, TSecond, TResult> func)
+        {
+            foreach (TFirst elem in set)
+            {
+                foreach (TSecond elem2 in others)
+                {
+                    yield return func(elem, elem2);
+                }
+            }
+        }
+    }
+}