Replace citation keys

[RiccardoBuscicchio]

Hello @yymao, thanks for your package. It has saved me quite some time recently. I appreciate your work.

I would like to ask you for a new functionality which I believe would be trivial to implement. With some guidance from you, I'd be happy to make a draft pull request.

I would like to have an additional flag in the main script (e.g. -k,--keys) to optionally:

1. replace the citation keys in the .tex file
2. replace the citation key in the .bib, accordingly

with the one in ADS, when processed.

Would this be doable? Thanks