Packets should derive Clone

[jeff-hiner]

Self-explanatory. I'm writing some tokio code right now that needs to take ownership of a PublishPacket to send it in a Future. I need to clone the packet before sending, in case I need to resend with DUP set. Should be as simple as adding Clone to the #[derive(...)] fields for each struct, and the VariablePacket enum.

[zonyitoo]

Hmm. That's true. Could you provide a PR?

[jeff-hiner]

Here ya go:

#27

[zonyitoo]

Merged.