rustls_root_cert_store_new

Create a rustls_root_cert_store. Caller owns the memory and must eventually call rustls_root_cert_store_free. The store starts out empty. Caller must add root certificates with rustls_root_cert_store_add_pem. <https://docs.rs/rustls/0.20.0/rustls/struct.RootCertStore.html#method.empty>