samples: add Terra samples

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

samples/Terra/macrokey.t

@@ -0,0 +1,9 @@
+
+what = function() return "abcd" end
+
+terra foo()
+  var a =   { [what()] = 4 }
+  return a.abcd
+end
+local test = require("test")
+test.eq(foo(),4)