Eventlet 0.20.0 released

[Sergey Shepelev]

Eventlet is a concurrent networking library for Python that allows you to change how you run your code, not how you write it.

https://pypi.python.org/pypi/eventlet/0.20.0

Important backward incompatible changes:
- removed select.poll(). We never had green poll implementation. If you really need blocking poll, use patcher.original('select').
- DNS resolving is always green with dnspython bundled in. This is just a nice free improvement. Be alert only if you intentionally wanted blocking resolving.

Other goodies:
* greenio: only trampoline when we block
* convenience: listen() sets SO_REUSEPORT when available; Thanks to Zhengwei Gao
* ssl: Fix "TypeError: read() argument 2 must be read-write bytes-like object, not None"
* greenio: _recv_loop behaviour with recv_into on closed sock
* ipv6: getaddrinfo would fail with scope index
* green.zmq: Support {send,recv}_{string,json,pyobj} wrappers
* greendns: Return answers from /etc/hosts despite nameserver errors
* patcher: fixed green existing locks fail (Python3)
* Add DAGPool, a dependency-driven greenthread pool
* wsgi: Unix socket address representation; Thanks to Samuel Merritt
* tpool: isolate internal socket from default timeout; Thanks to Alex Villacís Lasso
* wsgi: only skip Content-Type and Content-Length headers (GH-327)
* wsgi: 400 on blank Content-Length headers (GH-334)
* greenio: makefile related pypy socket ref counting
* ssl: Fix recv_into blocking when reading chunks of data
* websocket: support Gunicorn environ['gunicorn.socket']

Our website: http://eventlet.net/ 

Try latest version with `pip install -U eventlet`