bool ds_separate (const struct string *src, struct substring delimiters,
size_t *save_idx, struct substring *token);
bool ds_tokenize (const struct string *src, struct substring delimiters,
bool ds_separate (const struct string *src, struct substring delimiters,
size_t *save_idx, struct substring *token);
bool ds_tokenize (const struct string *src, struct substring delimiters,