Add smiley support :D

I noticed that when I tried to send smiley faces through [IRCanywhere](https://github.com/ircanywhere/ircanywhere)'s web interface, they came up half-decapitated from the the eyes up. I traced the culprit back to `irc-socket`. This patch stops this bloodshed by adding an extra `:` when the last parameter to a message starts with `:`.

Note that this [pull request to `irc-message`](https://github.com/expr/irc-message/pull/12) is pretty similar too. Let's bring back the laughter to IRC.