rem: head (const char *filename, int fd, uintmax_t n_units, int count_lines)
add: head (const char *filename, int fd, uintmax_t n_units, bool count_lines, bool elide_from_end)
context: head (const char *filename, int fd, uintmax_t n_units, int count_lines){  if (print_headers)    write_header (filename);  if (count_lines)    return head_lines (filename, fd, n_units);  else    return head_bytes (filename, fd, n_units);}