Relax ct_token_map signature to allow Borrow refs.

[ratmice]

I believe that changing the signature for the ct_token_map function should be fully backwards compatible,

1. it adds no additional generic types so turbofish should still work the same.
2. Because of the following blanket trait impl it should still accept all &HashMap<String, Storaget> instances.
   https://doc.rust-lang.org/stable/std/borrow/trait.Borrow.html#impl-Borrow%3CT%3E-for-%26T

Thus my belief is that this just relaxes the type signature to allow additional parameters like Box or Rc without having to first convert it to a reference type.