Reply command about yossarian-bot

[woodruffw]

That would probably require a fair bit of state, which isn't ideal for three reasons:

• yossarian-bot shoots all queued mail at once, making the semantics of a !reply command murkier when there are messages from multiple users.
• Lots of people send one-time messages and don't expect a response.
• The current command structure is set up as !<command> <subcommands ...>, where <command> maps directly to a plugin class (e.g., ping -> Ping). Thus it would have to be !mail reply or something like that, which feels ugly compared to !mail <nick> <your response>.

Good idea though, and useful from a user's standpoint. If I ever get around to rewriting this bot, this would be good to have in some form.