net/win32-ssl: a native Windows SSL layer

This implementation of SSL ports is less complete than `openssl', but
it's complete enough to drive HTTPS, and so it can be used to download
a package that provides the DLLs needed for the `openssl' library.

The `net/url' library uses `net/win32-ssl' on Windows when `openssl'
is not available (due to the absence of the OpenSSL DLLs).