Private polls

[jcgruenhage]

Private polls would be really helpful for some situations. Basically, the bot could send all users invites to a private chat, they vote there, and the result is posted after the poll is completed.

[shawnanastasio]

This is a really good idea. Unfortunately I don't have the time to implement it just yet, but I hope to get to it in the near future.

In the meantime, if someone wants to submit a PR I'd be more than willing to take a look at it.