void silc_mime_add_field(SilcMime mime,
                             const char *field, const char *value);

    Adds a field indicated by `field' to MIME message `mime'.  The field
    value is `value'.

    silc_mime_add_field(mime, "MIME-Version", "1.0");
    silc_mime_add_field(mime, "Content-Type", "image/jpeg");
    silc_mime_add_field(mime, "Content-Transfer-Encoding", "binary");