v2.0.1

• Making scopes optional on Google Compute Engine AppAssertionCredentials
  and adding a warning that GCE won't honor scopes (#419)
• Adding common sign_blob() to service account types and a
  service_account_email property. (#421)
• Improving error message in P12 factory
  ServiceAccountCredentials.from_p12_keyfile when pyOpenSSL is
  missing. (#424)
• Allowing default flags in oauth2client.tools.run_flow()
  rather than forcing users to create a dummy argparser (#426)
• Removing oauth2client.util.dict_to_tuple_key() from public
  interface (#429)
• Adding oauth2client.contrib._appengine_ndb helper module
  for oauth2client.contrib.appengine and moving most code that
  uses the ndb library into the helper (#434)
• Fix error in django_util sample code (#438)