Returns index.csv from the configured registry root or from GitHub.
When the index has no handle column, one is derived from each row's
folder field.
Value
A data frame containing replication metadata (folder, doi,
title, journal, year, authors, repo, and handle when present).
Examples
if (FALSE) { # \dontrun{
head(load_index()[, c("handle", "doi", "title")])
} # }