Namespace dpp::detail::std_coroutine: Remove and use std when all supported libraries have coroutines in it
Class dpp::message_file_data: Change the naming of this and make stickers (and potentially anything else that has data like this) use this.
Member dpp::message_file_data::mimetype: Look at turning this into an enum? This would allow people to easily compare mimetypes if they happen to change.