Add message_snapshots on Message

[jamesbt365]

Fixes #2995, as sending messages doesn't seem to be documented unless i missed something? Either way its out of scope if additional documentation is needed, that can be handled at a later date.

Had to write a custom deserialize function because for whatever reason Discord has nested the field, I'm not sure if this means they want to add more in the future, either way working with the nested field seems a bit unusual to the user.

If deserializing it this way is not a good idea We can nest it instead, though if the function can be made any more efficient that would be great too.