ScheduledEvent Support

[thewilloftheshadow]

https://discord.com/developers/docs/resources/guild-scheduled-event

This will need the following:

• ScheduledEvent class that can be partial (id + guild ID) with a fetch() call
• Client#fetchScheduledEvent
• An edit function on the ScheduledEvent
• A delete function on the ScheduledEvent
• A way to create a new ScheduledEvent from scratch (potentially on the Guild class as a guild.createScheduledEvent(), may need to see how the typings work out)
• A getUsers function on the ScheduledEvent
• Getter properties on the ScheduledEvent for the guild, channel, etc