samples: add Terra samples

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

samples/Terra/simpleadd.t

@@ -0,0 +1,15 @@
+struct Complex { real : float, imag : float }
+
+terra Complex.metamethods.__add(a : Complex, b : Complex)
+    return Complex { a.real + b.real, a.imag + b.imag }
+end
+
+
+terra foo()
+    var a = Complex { 1, 2 }
+    var b = Complex { 3, 4 }
+    var c = a + b
+    return c.real,c.imag
+end
+
+print(foo())