samples: add Terra samples

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

samples/Terra/compilecallback.t

@@ -0,0 +1,16 @@
+
+local a = 0
+local foo = macro(function(arg)
+	bar:gettype(function()
+		a = bar()
+	end)
+	a = 1
+	return 3
+end)
+
+terra bar()
+	return foo()
+end
+
+assert(bar() == 3)
+assert(a == 3)