Bot: Custom NameFlag handlers

[diamondburned]

Since some NameFlags would be either pretty tedious or straight up impossible to implement without making the code a mess, I propose a pluggable NameFlag handler API.

This would close #22.

Current Proposal

type NameFlagHandler interface {
	HandleEvent(v interface{}) error
	HandleMessage(g *gateway.MessageCreateEvent) error
}

type Handlers map[rune]NameFlagHandler

[diamondburned]

Closed in favor of #24.