Eventlet

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* Fix compatibility with SSLContext usage >= Python 3.7
* wsgi: Fix header capitalization on py3
* Fix 508: Py37 Deadlock ThreadPoolExecutor (598)
* drop Python 3.4 support
* Fix misc SyntaxWarning's under Python 3.8
* Remove unnecessary assignment in _recv_loop (601)

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* green.ssl: redundant set_nonblocking() caused SSLWantReadError

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* wsgi (tests): Stop using deprecated cgi.parse_qs() to support Python 3.8; Thanks to Miro Hrončok
* os: Add workaround to `open` for pathlib on py 3.7; Thanks to David Szotten

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* wsgi: Only send 100 Continue response if no response has been sent yet; Thanks to Tim Burke
* wsgi: Return 400 on negative Content-Length request headers; Thanks to Tim Burke
* Make a GreenPile with no spawn()s an empty sequence; Thanks to nat-goodspeed
* wsgi: fix Input.readlines when dealing with chunked input; Thanks to Tim Burke
* wsgi: fix Input.readline on Python 3; Thanks to Tim Burke
* wsgi: Stop replacing invalid UTF-8 on py3; Thanks to Tim Burke
* ssl: Fix compatibility with Python 3.7 ssl.SSLSocket; Thanks to Junyi
* reimport submodule as well in patcher.inject; Thanks to Junyi
* use Python 2 compatible syntax for keyword-only args; Thanks to nat-goodspeed
* wsgi: Catch and swallow IOErrors during discard(); Thanks to Tim Burke
* Fix for Python 3.7; Thanks to Marcel Plch
* Fix race that could cause using epolls as default hub even when platform does not support it; Thanks to Sergey Shepelev
* wsgi: make Expect 100-continue field-value case-insensitive; Thanks to Julien Kasarherou
* greenthread: optimize _exit_funcs getattr/del dance; Thanks to Alex Kashirin
* New benchmarks runner; Thanks to Sergey Shepelev
* ssl: fix connect to use monotonic clock for timeout; Thanks to Sergey Shepelev

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* greendns: don't contact nameservers if one entry is returned from hosts file; Thanks to Daniel Alvarez

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* greendns: Fix infinite loop when UDP source address mismatch; Thanks to Lon Hohberger
* greendns: Fix bad ipv6 comparison; Thanks to Lon Hohberger
* wsgi: Use byte strings on py2 and unicode strings on py3; Thanks to Tim Burke
* pools: put to empty pool would block sometimes; Thanks to Sam Merritt
* greendns: resolving over TCP produced ValueError; Thanks to Jaume Marhuenda
* support.greendns: ImportError when dns.rdtypes was imported before eventlet; Thanks to Jaume Marhuenda
* greendns: full comment lines were not skipped; Thanks to nat-goodspeed
* Drop support for Python3.3; Python2.6 and python-epoll package
* external dependencies for six, monotonic, dnspython; Thanks to nat-goodspeed
* wsgi: Don't strip all Unicode whitespace from headers on py3; Thanks to Tim Burke