Uploading large files

[sjkaliski]

First off, love this project!

It seems that the Upload flow is missing two parts in order to support large/async file uploads.

1. Specifying media_category in the INIT request
2. Checking media status (Twitter API Docs). This enables the application to check if the media is processed before attaching to a tweet.

Is there plans to introduce this? I'm happy to submit a PR.

[sjkaliski]

#211