Add `split-by-file` option

[pavelzw]

When providing multiple paths (or a path glob), i would like to create multiple comments instead of concatenating all into one comment.

This would also solve #1395 for me.

[marocchino]

I am not currently planning to support multiple comments for dynamic range, as they are difficult to implement. I recommend using metrix or other functions to write to different headers.

[pavelzw]

matrix has the issue that the comments might not be printed in order