* Add provider for US National Bureau of Economic Research
([27](https://github.com/GjjvdBurg/paper2remarkable/pull/27)).
* Automatically extract the filename from a pdf url where possible
([25](https://github.com/GjjvdBurg/paper2remarkable/issues/25)).
* Speed up centering of pdfs by removing unnecessary cropping operation.
* Improve robustness against missing metadata, remove spaces in author names,
and other minor improvements.