switch to static linking on windows and update installation page

fixes #1121

crypt32, gdi32, user32, and ws2_32 are required to make it statically link successfully, but are not required for dynamic linking.

At the moment this results in a wheel that is ~978k for 64-bit windows (as opposed to 248kb for our previous release). Not a big deal.
We'd have to conditionally add `Cryptography_STATIC_OPENSSL` (or maybe `Cryptography_PYCA_OPENSSL_INSTALL` to match the env var name?) based on whether it was Windows or not since right now this flag only affects Windows.

Anybody have an opinion? Should we do this? Should we punt for post-0.5?