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/language/inheritance/inherit_methods.wren

@@ -0,0 +1,26 @@
+class Foo {
+  methodOnFoo { IO.print("foo") }
+  method(a) { IO.print("foo") }
+  method(a, b, c) { IO.print("foo") }
+  override { IO.print("foo") }
+}
+
+class Bar is Foo {
+  methodOnBar { IO.print("bar") }
+  method(a, b) { IO.print("bar") }
+  method(a, b, c, d) { IO.print("bar") }
+  override { IO.print("bar") }
+}
+
+var bar = new Bar
+bar.methodOnFoo // expect: foo
+bar.methodOnBar // expect: bar
+
+// Methods with different arity do not shadow each other.
+bar.method(1) // expect: foo
+bar.method(1, 2) // expect: bar
+bar.method(1, 2, 3) // expect: foo
+bar.method(1, 2, 3, 4) // expect: bar
+bar.override // expect: bar
+
+// TODO: Prevent extending built-in types.