Allow multiple inputs in single call - enhancement request

[robchallen]

I'd like to be able to POST a list of DOIs to the api and get a set of all citations of those DOIs or all references of those DOIs back.

Probably for your server's sake this should be combined with some sort of limit parameter. I don't understand the SPARQL well enough to know how to do this via the endpoint but I think it would be possible.

I can send each DOI separately but think it would be better to do in bulk.