Improve event handling

[s1kx]

Since discordgo does not have a common interface amongst Events or a name/ID attached to them, it's only possible to handle events selectively with type switches or reflection.
Type switches get messy, and reflection is slow.

We should implement

• EventType - enum to denominate an Event, corresponding to each discordgo Event
• GetEventType() - function to determine the type of a given event
• DiscordEvent - wrapper class for discordgo Events, including fields such as EventType and possibly introducing new ones such as EventGroup, Tags
• EventDispatcher - handles dispatching events to hooks only when they are subscribed to them

[s1kx]

New event system is in place with events subpackage handling event types, and the EventDispatcher being responsible for sending events to the appropriate hooks.