refdox: Base16, Base32, and Base64 Data Encodings

A number of places in https://git.torproject.org/tor.git https://git.torproject.org/torspec.git refer to an obsoleted info rfc https://tools.ietf.org/html/rfc3548.html which should probably be repointed to the track rfc https://tools.ietf.org/html/rfc4648.html which has handy test vectors, etc.

find | xargs grep 3548

Also, there doesn't seem to be a torspec/docs "component" in trac to pick, so I picked the client.