refactor/feat: rewrite certs::fingerprint with generic data type…

…and allowing different bin2txt (getting ready for DANE)

examples/simple.rs

@@ -1,6 +1,6 @@
 use tokio_gemini::{
     certs::{
-        fingerprint::{generate_fingerprint, Algorithm},
+        fingerprint::{self, CertFingerprint},
         SelfsignedCertVerifier,
     },
     Client, LibError,
@@ -47,7 +47,7 @@ impl SelfsignedCertVerifier for CertVerifier {
         eprintln!(
             "Host = {}\nFingerprint = {}",
             host,
-            generate_fingerprint(cert, Algorithm::Sha512),
+            CertFingerprint::<fingerprint::Sha256>::new(cert).base64(),
         );
         Ok(true)
     }