textbuf_append_char
textbuf_append_char(itb, '\0');
static void textbuf_append_char(idm_textbuf_t *itb, char c);
textbuf_append_char(itb, '=');
textbuf_append_char(itb, '=');
textbuf_append_char(itb, '=');
textbuf_append_char(itb, idm_hex_to_ascii[(n >> 4) & 0xf]);
textbuf_append_char(itb, idm_hex_to_ascii[n & 0xf]);
textbuf_append_char(itb, '=');
textbuf_append_char(itb, '=');
textbuf_append_char(itb, ',');