Remove duped fields in irc.Event

[belak]

Currently irc.Event has a number of duplicated fields.

Event.Prefix is the same as Event.Identity.Raw. You can even infer the Event.Prefix from Event.Identity.

I would like to remove Event.Identity and replace it with Event.SplitPrefix() (nick, user, host string)

Any comments, or ideas on how to make this better? This does have the unfortunate side effect of possibly requiring the parsing of Event.Prefix multiple times, though I don't think that should be a huge issue.

[belak]

Just wanted to note that this is in preparation for adding stringers to the Event struct. In its current state, that would be fairly annoying as there is not a single source of truth for the prefix. This would move that source of truth into Event.Prefix

[belak]

This will be fixed when pr #10 goes in