Convert references file from Bibtex to CSL-JSON

[joshwlambert]

There is a general convention of Epiverse packages to move from using Bibtex (.bib files) for storing references used in our R packages to using CSL-JSON (.json).

The original driver of this change is to ensure that Github linguist correctly identifies Epiverse packages as R packages instead of TeX or markup packages, as .bib is considered markup by linguist whereas CSL-JSON is considered data and ignored.

This change has already been implemented in {finalsize} (epiverse-trace/finalsize#155, epiverse-trace/finalsize#156).