Update to handle message parsing closer to the irc spec

Note that I also added a (mostly) backwards compatible mode, which will allow users to update one line in the config and change calls of .Message to .Message() and have their old code work. It stores the message in the event along with a bool representing if it's the old style parsing or not.

It's worth noting that there may be a better way of doing this, but it would require a bit more breakage, such as storing the Arguments in something called Args, and having .Arguments() grab the correct slice based on the parsing style. This causes issues though because there isn't always a Message.

If you'd like, I can remove the compatibility code and just leave the .Arguments in, as that would be the cleanest solution. I just felt like it would be good to have a fallback option, just in case.

This would close #18