samples: add Terra samples

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

samples/Terra/scope.t

@@ -0,0 +1,13 @@
+terra scope()
+    var a = 4
+    var b = 0
+    b = b + a
+    do
+        var a = 5
+        b = b + a
+    end
+    b = b + a
+    return b
+end
+local test = require('test')
+test.eq(scope(),13)