Implement efficient conversion from String, Vec<u8> and &[u8] for identifiers

[mina86]

Let’s look at ClientId for example. Suppose I have a client id as a String. There’s currently no way to convert that String into ClientId without performing an allocation. The two available constructors are ClientId::from_str (which takes a str slice and then allocates a string) and Client::new (which takes client type and counter and than formats a new id).

The feature request is to provide TryFrom implementations for the identifiers which take ownership of the passed String.

Going further, I’d also love to see constructors which take Vec and &[u8] arguments and skip UTF-8 verification checking. Currently, user has to first get a String or &str and then pass that to identifier’s constructor. However, constructors already check if the string consists of valid characters so they might work on byte slices just as easily and after performing verification convert them to strings.