Make options.parse_config_file supporting custom encoding
Assume all config files are encoded in UTF-8
Split overview.rst into separate files.
Set version number to 4.0b2
Fix binary websocket connections
Merge pull request #1091 from xose/patch-1

Fix binary websocket connections
Merge branch 'master' of github.com:tornadoweb/tornado
Add tests for both binary and unicode messages in websockets.
Disable twisted tests on pypy on travis-ci since they seem to be flaky.

They were already disabled in tox.ini.
Expand and rewrite the guide docs.
Merge branch 'guide'

* guide:
  Expand and rewrite the guide docs.
  Split overview.rst into separate files.
Rewrite chatdemo to use a coroutine instead of callbacks.
Add a test for exception in websocket callbacks.
Fix outdated variable name in docs.
Remove length requirement from v1 XSRF tokens
Turn short and hex XSRF tests into success tests
Don't raise when failing to hex decode XSRF v1
Catch `binascii.a2b_hex` errors on Python 3
Merge remote-tracking branch 'tictail/branch3.2'

Closes #1097
Add XSRF change to the release notes.