SilcSFTP silc_sftp_client_start(SilcStream stream,
                                    SilcSchedule schedule,
                                    SilcSFTPVersionCallback version_cb,
                                    SilcSFTPErrorCallback error_cb,
                                    void *context);

    Starts SFTP client and returns context to it.  The version callback
    indicated by the `version_cb' will be called after the SFTP session has
    been started and server has returned the version of the protocol.  The
    SFTP client context is returned in the callback too.  This returns the
    allocated SFTP client context or NULL on error.  The `stream' will be
    used to read and write the SFTP packets.  The `error_cb' will be called
    in case a stream error occurs, such as end of stream.