samples: add Terra samples

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

samples/Terra/signext.t

@@ -0,0 +1,12 @@
+
+
+terra bar()
+	var a : uint8 = 255
+	var b = foo(a)
+	return a == b
+end and
+terra foo(a : uint8)
+	return a
+end
+
+print(bar())