aiohttp 0.16.0 release

Major release, new features added.

Client API refactored a bit, ClientSession is first-class citizen now and highly recommended to use instead of aiohttp.request.

Full list of changes:

• Unset waiter future after cancellation #363
• Update request url with query parameters #372
• Support new fingerprint param of TCPConnector to enable verifying
  ssl certificates via md5, sha1, or sha256 digest #366
• Setup uploaded filename if field value is binary and transfer
  encoding is not specified #349
• Implement ClientSession.close() method
• Implement connector.closed readonly property
• Implement ClientSession.closed readonly property
• Implement ClientSession.connector readonly property
• Implement ClientSession.detach method
• Add __del__ to client-side objects: sessions, connectors,
  connections, requests, responses.
• Refactor connections cleanup by connector #357
• Add limit parameter to connector constructor #358
• Add request.has_body property #364
• Add response_class parameter to ws_connect() #367
• ProxyConnector doesn't support keep-alive requests by default
  starting from now #368
• Add connector.force_close property
• Add ws_connect to ClientSession #374
• Support optional chunk_size parameter in router.add_static()