samples: add Terra samples

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

samples/Terra/constant2.t

@@ -0,0 +1,21 @@
+
+
+local a = terralib.new(int,3)
+local b = terralib.new(int8,4)
+local c = terralib.new(int64,5)
+local d = terralib.new(float,3.25)
+local e = terralib.new(double,4.25)
+
+f = global(4)
+terra foo()
+	return &f
+end
+
+local pf = foo()
+
+terra bar()
+	return a + b + c + d + e + @pf
+end
+
+local test = require("test")
+test.eq(bar(),23.5)