Use uppercase hex digits in database and API.

- Both Sequoia and GnuPG create query strings with uppercase hex
    digits.  By using uppercase in the filesystem and new API, we can
    serve keys using nginx.

README.md

@@ -43,9 +43,10 @@ Hagrid has it's own URL scheme to fetch keys, verify user IDs and delete keys.
 It's meant to be machine readable, but it's not a REST API. The following URLs
 are handled.
 
-- `GET /by-fingerprint/<fingerprint>` retrieves the key with the given
-  fingerprint.
-- `GET /by-keyid/<key ID>` retrieves the key with the given long key ID.
+- `GET /by-fingerprint/<FINGERPRINT>` retrieves the key with the given
+  fingerprint.  Hexadecimal digits must be uppercase.
+- `GET /by-keyid/<KEY-ID>` retrieves the key with the given long key
+  ID.  Hexadecimal digits must be uppercase.
 - `GET /by-email/<URL-encoded user ID>` retrieves the key with the given user
   ID. Only exact matches are accepted.
 - `GET /vks/verify/<token>` verifies a user ID using a token string send by

examples/import.rs

@@ -160,14 +160,14 @@ impl Filesystem {
 
     /// Returns the path to the given KeyID.
     fn path_to_keyid(&self, keyid: &openpgp::KeyID) -> PathBuf {
-        let hex = keyid.to_hex().to_lowercase();
+        let hex = keyid.to_hex();
         self.base_by_keyid.join(&hex[..2]).join(&hex[2..])
     }
 
     /// Returns the path to the given Fingerprint.
     fn path_to_fingerprint(&self, fingerprint: &openpgp::Fingerprint)
                            -> PathBuf {
-        let hex = fingerprint.to_hex().to_lowercase();
+        let hex = fingerprint.to_hex();
         self.base_by_fingerprint.join(&hex[..2]).join(&hex[2..])
     }
 

src/types.rs

@@ -56,7 +56,7 @@ impl TryFrom<sequoia_openpgp::Fingerprint> for Fingerprint {
 
 impl ToString for Fingerprint {
     fn to_string(&self) -> String {
-        hex::encode(&self.0[..])
+        hex::encode_upper(&self.0[..])
     }
 }
 
@@ -133,7 +133,7 @@ impl From<Fingerprint> for KeyID {
 
 impl ToString for KeyID {
     fn to_string(&self) -> String {
-        hex::encode(&self.0[..])
+        hex::encode_upper(&self.0[..])
     }
 }