Regex and Simple (Prefix) commands. Commands and Handlers are backed by container/list.

This is a pretty big change, but its mostly related to dispatch.go.

The bot now supports commands that are matched by a regex.
The matching has priority, in my example I have two commands, one listens for any URL's, the other listens for YouTube specific URL's. The YouTube one will match first, and be handled.

I also implemented the legacy prefix commands with the same system, but the API changed to "SimpleCommand" and "SimpleCommandHelp" (for automatic help responses).

The other files changed are just to use constants, you can choose to reject that portion, but it makes the code a lot cleaner IMO.

I really like these changes, I hope you strongly consider adding them.