feat: remove newlines at the beginning of a file

[logic-finder]

For example:

$ cat demo.c

int main(void){return 0;}
$ proofread -b --dry-run - < demo.c
> proofread -b --dry-run=full -
=================================================
   1|-\n
   2|int main(void){return 0;}

This feature may be not that useful, though.