Fix issue of redundant oauth rebuilding when redirects

- Add support for request token and access token in json format. For example in [Kuaipan.cn API] (http://www.kuaipan.cn/developers/document_oauth.htm).
- Add verifier parameters to OAuth1Session.fetch_access_token() for convenience.
- Fix issue of redundant oauth rebuilding when binary response without authorization after redirects.
It's commented out, but probably better to delete.