Refactoring handshake/hybi.py
Refactoring handshake/hybi.py

There is no change in behavior. Make Handshaker class reusable for
implementing multiplexing extension.

- Extract creating handshake response from _send_handshake
  as _create_handshake_response.
- Add _create_stream method that creates a Stream object.
  A subclass may override the method.

BUG=none
TEST=test/run_all.py

Review URL: https://codereview.appspot.com/6329047

git-svn-id: d23f85197b9dafcb1b1682eb9d0eda70517bdc52@642 4ff78f4a-9131-11de-b045-6380ec9940d4

bpsinc-native/src_third_party_pywebsocket_src,bpsinc-native/src_third_party_pywebsocket_src,bpsinc-native/src_third_party_pywebsocket_src,bpsinc-native/src_third_party_pywebsocket_src