add get_segment_efforts, allow passing in of request_session for easy override, and a bug fix

auto-fix of trailing whitespaces i isolated into dedicated commits to make code review easy.

the passing in of request_session, is so you can write client code that looks like this

  # code
  import requests
  import cachecontrol
  from cachecontrol.caches import FileCache
  rsession = cachecontrol.CacheControl(requests.Session(),
                                                               cache=FileCache('.web_cache', forever=True))

  client = Client(access_token=STORED_ACCESS_TOKEN, requests_session=rsession)