Support the new (Labs) endpoints

[tesaguri]

• Decide on the OAuth 2.0 client library to use (or extend tesaguri/oauth1-request-rs to support it)
  • What Twitter calls "OAuth 2.0" seems to use the access token type of "bearer" only, which is trivial enough to just implement in twitter_stream.
• Implement APIs behind an unstable feature flag
  • Filter
  • Sample
• Stabilize the new APIs and deprecate the current APIs after the new endpoints graduate out of Labs
• Remove the existing APIs after the current endpoints is closed

Links

• "New filtered stream endpoints available in Labs, and the future of statuses/filter - Announcements - Twitter Developers"
• "New sampled stream endpoint available in Labs - Announcements - Twitter Developers"
• Twitter Developers docs on the new filtered stream
• Twitter Developers docs on the new sampled stream