Cannot send private message

[kaedys]

Sending a message via the CreateMessage API endpoint allows calls with only an email or personID, which then sends the message as a private message. However, this library immediately errors during CreateMessage if the RoomID is not set. RoomID is only needed if sending a message to a channel, rather than a private message. This error case makes sending private messages impossible unless one knows the roomID for that private message, which prevents creating new private message conversations (as those have no roomID before the first message).