Lack of documentation for SharedSecret generation.

[Dominically]

I cannot figure out how to provide a type that implements Digest for creating a SharedSecret and there is no examples or documentation which show how to get a shared secret from a secret key and a public key (from a different key-pair). It would help if an example was provided as to how to generate a shared secret using ECDH with this library.

[undersquire]

You need to provide the hasher. For example, use the sha2 crate you should be able to provide the Sha512 as the type.