A simple, hacky command line utility for fetching article PDFs from
Sci-Hub, book PDFs from Libgen and formatted citations
from CrossRef from supplied DOIs and/or ISBNs.
Article download requires DOIs, while book downloads require ISBNs.
Citations, on the other hand, can be fetched both from DOIs and ISBNs,
although it should be noted that ISBNs are converted to DOIs
by querying CrossRef which sometimes fails, especially for
older books.