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add both base64 and base32 addresses as separate protocols, remove port from addresses to be expressed as /tcp, etc.

(bug caught by fuzzer)

fixes part one of #77

See [rfc4007].

Can be prefixed to "ip6" like so:

    /zone/eth0/ip6/fe80::1

This corresponds to the rfc4007 address `fe80::1%eth0`

[rfc4007] https://tools.ietf.org/html/rfc4007

Otherwise, .String() can panic.

Instead of having the transformers deal with variable length argument prefixes,
just do this in the bytesToString/stringToBytes functions.

Allowing multiaddr extensions to have data with