Reorganize tests and benchmark scripts.

Mainly to get rid of one top level directory. But this will
also be useful when there are tests of the embedding API.

test/core/list/reduce.wren

@@ -0,0 +1,14 @@
+var a = [1, 4, 2, 1, 5]
+var b = ["W", "o", "r", "l", "d"]
+var max = new Fn {|a, b| a > b ? a : b }
+var sum = new Fn {|a, b| a + b }
+
+IO.print(a.reduce(max)) // expect: 5
+IO.print(a.reduce(10, max)) // expect: 10
+
+IO.print(a.reduce(sum)) // expect: 13
+IO.print(a.reduce(-1, sum)) // expect: 12
+
+// sum also concatenates strings
+IO.print(b.reduce("Hello ", sum)) // expect: Hello World
+IO.print(b.reduce(sum)) // expect: World