samples: add Terra samples

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

samples/Terra/pointerarith.t

@@ -0,0 +1,31 @@
+terra foo(a : &int) : ptrdiff
+  var b : &int b = a + 10
+  return b-a
+end
+
+terra bar()
+  var b:int = 10;
+  return foo(&b)
+end
+
+terra foo2(a : &int) : &int
+  a = a + 6 
+  a = 3 + a
+  a = a + 10
+  return a
+end
+
+terra foo3(a : &int) : &int
+  a = a - 11
+  a = 2 + a
+  a = a - 10
+  return a
+end
+
+terra bar2(a : int)
+  return @(foo3(foo2(&a)))
+end
+
+local test = require("test")
+test.eq(bar(),10)
+test.eq(bar2(42),42)