samples: add Terra samples

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

samples/Terra/mathlib.t

@@ -0,0 +1,9 @@
+local c = terralib.includec("math.h")
+
+terra mysqrt(a : float)
+	return c.sqrtf(a)
+end
+
+local test = require("test")
+test.eq(mysqrt(4),2)
+test.eq(mysqrt(9),3)