Uploads media data and returns an ID string that can be used to attach media to Tweets

public func upload(mediaData: Data, mimeType: String, progress: UnsafeMutablePointer<Progress>? = nil)

• mediaData: The media data to upload
• mimeType: The type of media you're uploading
• progress: An optional pointer to a Progress instance, used to track the progress of the upload task. The progress is based on the number of base64 chunks the data is split into; each chunk will be approximately 2mb in size.

A MediaUploadResponse object containing information about the uploaded media, including its mediaIdString, which is used to attach media to Tweets