Encoding:
    SILC_ASN1_UTC_TIME(timeval)
    SILC_ASN1_UTC_TIME_T(opts, tag, timeval)

    Decoding:
    SILC_ASN1_UTC_TIME(&str, &timeval)
    SILC_ASN1_UTC_TIME_T(opts, tag, timeval)

    Macro used to encode or decode universal (UTC) time value.  The
    time value type is SilcTime.

    The `opts' is SilcAsn1Options.  The `tag' is a tag number.