- Remove 3.4
- Update to latest 3.x series
- Update to PyPy 7

Tests are not passing locally yet.

The build cache was the only thing keeping 3.7.0a4 around; it can no
longer be installed from pyenv. And I accidentaly deleted the master
build cache, so we have no choice.

It may be difficult to get 3.7b1 installed due to
https://github.com/travis-ci/travis-ci/issues/9069

No new unexpected failures.

Rename the 'async' methods and classes to 'async_'. I couldn't think
of a better name. But keep the old names available for BWC. Fixes #1047.

Move 3rd party libraries to deps/ directory.

Move gevent and greentest to src/ directory. This fixes tox.

At this point the builds should all work the same. Lets check.

Also update the test_ssl.py to cpython rev 2c9ff9e (head). This fixes the
problems with invalid certs for svn.python.org.

These tests include much more testing of the new-in-2.7.9 SSLContext
settings, which revealed some problems in our hostname validation, our
handling of read/write/do_handshake for closed sockets, and the missing
alpn_selected method.