Features
   * Add the function mbedtls_ssl_get_fatal_alert(), which returns the type of
     the last received fatal alert. This allows callers to retrieve more
     detailed information when mbedtls_ssl_handshake(),
     mbedtls_ssl_handshake_step(), or mbedtls_ssl_read() returns the generic
     MBEDTLS_ERR_SSL_FATAL_ALERT_MESSAGE error code.
