Support multi-line CAP requests and responses

[Ascrod]

Currently, Ambassador only supports receiving a single CAP ACK/CAP NAK line in response to a CAP REQ command. We should not only be able to handle multiple ACK/NAK responses at a time, but we should also be able to send multiple REQ commands.

On the request side, we should have the ability to put together a single command, split it if necessary, and send all the resulting commands, similar to what we do now with PRIVMSG and NOTICE.

On the response side, I believe we can count how many total caps we receive in ACK and NAK responses, assuming that the server will eventually ACK or NAK every cap we request. I don't like making this assumption, but I'm not sure how else we can tell we got everything without using a timeout, which I'd rather not do.