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.
Should this handle an empty string, as would happen with `env PYCA_OPENSSL_INSTAL=`?