md5 fingerprints not quite right

Currently you can parse the md5 "fingerprint": `59:a46:1:0e:38:18:9f:0f:28:58:2a:27:f7:65:c5:87`, which is not really valid (we'll just merge the "a46" and "1" together).

It might also be nice to tolerate input of the form "MD5:59:a4:61:e:38:18:9f:f:28:58:2a:27:f7:65:c5:87" with leading zeros removed.