Reformatted test code according to this heuristic:

http://blog.ploeh.dk/2013/06/24/a-heuristic-for-formatting-code-according-to-the-aaa-pattern
Reformatted test a bit,

to make it clearer to the reader that the actual value returned is another
visitor, but this time the Value is an Action.
Updated README with more succinct test example.