docs: topic names can be 64 instead of 32 characters

Can the [documentation](http://nsq.io/clients/tcp_protocol_spec.html) reflect that topic names can be up to 64 characters in nsq 0.2.28 and after? This discrepancy confused me for a little while in the pynsq tests, since nsq 0.2.27 rejected topic names > 32 characters.