Pmidcite

* Top of README more clean and succinct
* Add twitter badge and link

* Use external link for gh-page images so they are viewable from PyPi page
* Improve utility of function by returning a list of namedtuples instead of None

* Massive speed increase of downloading PMIDs returned from a PubMed query by downloading 1,000 PMIDs at a time 81a6cd8 e04a7c5

* Add CITATION.cff file
* Added Google Search Console tag
* Changed: minor updates, including:
* Return [] if there are no authors e294100

* Improve speed by 4x for "online-only" mode when downloading citation data for multiple papers and their citations and/or references
* Remove obsolete argument, `prt_icitepy`, of `PubMedQueryToICite`
* If an NIH citations contains no authors, use an empty list (e.g. []) git show e2941007b67fb8aae3ce861da7013a97811b6dcc (src/pmidcite/icite/api.py)

Changes for [Issue 5](https://github.com/dvklopfenstein/pmidcite/issues/5):
* Added "online-always" mode to download the latest NIH citation data three times as fast as the original "online/offline" mode
* Made "online-always" mode the default
* Moved "online/offline" mode to be an option