Bind SSL_CTX_set_client_hello_cb

[daurnimator]

https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_client_hello_cb.html

This new api replaces the older HostNameCallback.

Should support yielding via

A callback may also return a negative value to suspend the handshake, and the handshake function will return immediately.

Thanks to @drwilco for letting me know about this API.

[daurnimator]

See also SSL_CTX_set_cert_cb