Function to help craft fingerprint fields #21

It would be nice if there was a way to populate this structure from a standard *http.Request and *tls.ClientHelloInfo.

In Caddy 1, we were able to get both values in an HTTP request: https://github.com/caddyserver/caddy/blob/891446d06340db2912c9a970bfe862bd54efbb70/caddyhttp/httpserver/mitm.go#L64

However, I am afraid I will fill in the RequestFingerprint struct improperly, it would be super helpful if the lib could do that given the request and ClientHello info.