samples: add Terra samples

source: https://github.com/zdevito/terra/tree/master/tests

samples/Terra/metatype.t

@@ -0,0 +1,16 @@
+local function foo(T)
+    terra T:what()
+        return self.a + self.b
+    end
+end
+struct A(foo) {
+    a : int;
+    b : int;
+}
+
+terra test()
+    var a  = A {1,2}
+    return a:what()
+end
+
+assert(test() == 3)