Shorten fingerprint to fpr in the Filesystem db.

- This keeps relative links below 60 bytes, allowing ext4 to store
    the link in the inode itself.

nginx.conf

@@ -23,9 +23,9 @@ http {
     }
 
     location /by-fingerprint/ {
-      rewrite ^/by-fingerprint/([^/][^/])(..*)$ /by-fingerprint/$1/$2 break;
+      rewrite ^/by-fingerprint/([^/][^/])(..*)$ $1/$2 break;
       default_type application/pgp-keys;
-      try_files /$uri =404;
+      try_files /by-fpr/$uri =404;
     }
 
     location /by-keyid/ {

src/database/fs.rs

@@ -76,7 +76,7 @@ impl Filesystem {
         create_dir_all(base.join("scratch_pad"))?;
 
         let base_by_keyid = base.join("public").join("by-keyid");
-        let base_by_fingerprint = base.join("public").join("by-fingerprint");
+        let base_by_fingerprint = base.join("public").join("by-fpr");
         let base_by_email = base.join("public").join("by-email");
         create_dir_all(&base_by_keyid)?;
         create_dir_all(&base_by_fingerprint)?;