Enum for Channel and Message "type" property

[PsychoTea]

Channel, Message, and perhaps others have an integer "type" property which dictates some basic information about the object. At the moment it is passed as an integer, however we should instead reference this as an enum.

Docs References: Channel - https://discordapp.com/developers/docs/resources/channel#channel-object-channel-types Message - https://discordapp.com/developers/docs/resources/channel#message-object-message-types

[Slut]

Added #22