insert comments "calls" and "called by"

[moodymudskipper]

We might have a linter that inserts at the top of the body a comment that says which functions from the package call this function.

It needs to be a linter because we want to avoid possibilities of being out of sync
It's convenient to have it at the top of the body because this way we have it in the secret when debugging, and it doesn't clash with roxygen comments