Automatic use of strings defined in [krr.bib](https://github.com/krr-up/bibliography/blob/master/krr.bib)

[jorgefandinno]

Our README says

Use the strings defined in krr.bib for journal names.

example: @string{lncs = {Lecture Notes in Computer Science}} for use in BibTex entries as series = lncs

I have a small script that does this automatically and I am considering adding it to the bibfmt.py tool.

The results of applying it to the bibliography were merged in #217_

This is a pure formatting thing in the sense that the behavior of the bibliography does not change. Thus, it seems that adding it to the format subcommand is appropriate. This way, it also becomes part of the check to ensure compliance.

Thoughts?