call to_hash on object that respond to to_hash + specs

That's not a very clear description. Really, what happens is when you call `to_hash` on a Hashie object, it will deep convert everything to a hash. Now, if you have an object that's not a `Hash`, but responds to `to_hash`, it will convert that too. I think this should read something like this: "Hash#to_hash will also convert nested objects that implement `to_hash`". 

What do you think?