Create API endpoint to invite guest user to room

Problem Definition

There isn't an API endpoint to invite guest users to rooms with guest access enabled.

Suggested Solution

Provide an API endpoint that would get a room and email(s) as parameters and send emails from Hipchat to guest users by email address.

Workaround

1. Create room with guest access enabled or enable guest access for an existing room via Update room
2. Get the room's guest URL via Get room
3. Share the room's guest URL with the guest user via email or UI