Adding methods for Scheduled Events

[juststephen]

Made using the Discord API documentation: https://discord.com/developers/docs/resources/guild-scheduled-event#guild-scheduled-event

These is a starting point for scheduled event integration.

Summary

Added:

• list_scheduled_events
• create_scheduled_events
• get_scheduled_event
• modify_scheduled_event
• delete_scheduled_event
• get_scheduled_event_users

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR adds something new (e.g. new method or parameters).

[4Kaylum]

Merging the PR because it just changes the HTTP methods - no documentation is fine because they aren't publicly exposed. Thanks for adding these.