Add Random.shuffle().

test/random/shuffle.wren

@@ -0,0 +1,23 @@
+import "random" for Random
+
+var random = Random.new(12345)
+
+// Empty list.
+var list = []
+random.shuffle(list)
+System.print(list) // expect: []
+
+// One element.
+list = [1]
+random.shuffle(list)
+System.print(list) // expect: [1]
+
+// Given enough tries, should generate all permutations.
+var hits = {}
+for (i in 1..200) {
+  var list = [1, 2, 3, 4]
+  random.shuffle(list)
+  hits[list.toString] = true
+}
+
+System.print(hits.count) // expect: 24