Implement Base32 Hash hostnames, via the naming service.
Names are of the form [52-characters].i2p, where
the 52 characters are the Base32 representation of our
256-byte hash. The client requests a lookup of the hash
via a brief I2CP session using new I2CP request/reply
messages. The router looks up the leaseset for the hash
to convert the hash to a dest. Convert the I2PTunnel
'preview' links to use Base32 hostnames as a
demonstration.