TLS support for tokio-postgres via openssl.

Example

use openssl::ssl::{SslConnector, SslMethod};
use tokio_postgres_openssl::MakeTlsConnector;

let mut builder = SslConnector::builder(SslMethod::tls()).unwrap();
builder.set_ca_file("database_cert.pem").unwrap();
let connector = MakeTlsConnector::new(builder.build());

let connect_future = tokio_postgres::connect(
"host=localhost user=postgres sslmode=require",
connector,
);

// ...