CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS will now suppress link flags regardless
of platform. Additionally, CRYPTOGRAPHY_WINDOWS_LINK_LEGACY_OPENSSL is
now the flag you need if you want to link against < 1.1.0 on windows.

* time to remove commoncrypto, fare thee well

* remove even more

* update the changelog

* remove more things

* don't need this function

* remove CAST5 CTR tests since that was only supported in commoncrypto

* assert a thing

* Clarified Windows development installation and doc'd upstream enchant bug

* Fixed whitespace problems

* Fixed merge resolution mistake

* Update getting-started.rst to clarify OS X Homebrew pip install
On OS X El Capitan following the current instructions fails with fatal error: 'openssl/opensslv.h' file not found on pip install -r dev-requirements.txt; this change adds to the instructions to clarify that CFLAGS and LDFLAGS may need to be set. I based this on the instructions in the Installation page.

* Address reaperhulk comments, OpenSSL must be installed.

Clarify that OpenSSL must be installed via Homebrew or MacPorts and how to build statically.

* Make Homebrew, MacPorts, OpenSSL links

* Fix doc errors and improve overall flow
Insert tip about tox needing the same flags
Make console example multi-line so that pip install is visible
Change heading levels to allow OS X sub-section