samples: add Terra samples

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

samples/Terra/pow.t

@@ -0,0 +1,28 @@
+local N = 4 -- N is a Lua variable
+terra powN(a : double)
+    var r = 1
+    for i = 0, N do
+        r = r * a
+    end
+    return r
+end
+
+
+
+
+local math = {}
+for N = 1,10 do
+    math["pow"..tostring(N)] = terra(a : double)
+        var r = 1
+        for i = 0, N do
+            r = r * a
+        end
+        return r
+    end
+end
+
+local test = require("test")
+test.eq(powN(3),81)
+test.eq(math.pow1(2),2)
+test.eq(math.pow2(2),4)
+test.eq(math.pow3(2),8)