samples: add Terra samples

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

samples/Terra/cast.t

@@ -0,0 +1,11 @@
+terra bar(a : int) : int
+    return a + 1
+end
+terra foo(a : int) : int
+    
+    return a
+end
+
+local test = require("test")
+test.eq(foo(2),2)
+test.eq(bar(2),3)