Add ed2k hash type

[Artoria2e5]

ed2k is a protocol that had quite some significance. Compared to torrent-info it has the advantage of identical files always yielding the same hash, since there's nothing tweakable in it. As with the case of torrent, it might have some value in eventually being addressable by ipfs.

A related, stronger hash is the AICH hash tree used by eMule. This is a merkel tree used for error correction, but being built out of SHA-1 it suffers from slightly fewer security complaints.

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In the same line of incorporating P2P hashes, Gnutella, G2, Gnunet, Freenet et al. can also each use a type.