samples: add Terra samples

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

samples/Terra/explicitcast.t

@@ -0,0 +1,11 @@
+
+terra foo()
+    var a : int64 = 256+3
+    var c = intptr(&a)
+    var d = [&int64](c)
+    var fi = int(true)
+    var what = @[&int8](&a)
+    return @d,fi,what
+end
+local test = require("test")
+test.meq({256+3,1,3},foo())