@param str String to be parsed
@param beg Set on return to the 0-based start of the region
@param end Set on return to the 1-based end of the region
@return Pointer to the colon or '\0' after the reference sequence name,
or NULL if @a str could not be parsed.
@param str String to be parsed @param beg Set on return to the 0-based start of the region @param end Set on return to the 1-based end of the region @return Pointer to the colon or '\0' after the reference sequence name, or NULL if @a str could not be parsed.