Prepare for CRAN release

[billdenney]

No description provided.

[billdenney]

Comment from CRAN:

Please write references in the description of the DESCRIPTION file in the form
authors (year) doi:...
(If you want to add a title as well please put it in quotes: "Title")
So please add authors and (year) as well.

Please always explain all acronyms in the description text. -> HiSCR,, HASI-R, PGA, IHS4

@DBartlettHP , can you please make the requested changes to the DESCRIPTION file in this branch? The author names would be "last name" if a single author, "last name and last name" if two authors, or ""first author's last name, et al" if more than two authors.

[billdenney]

@DBartlettHP, I think that the indentation under the "Description" needs to be consistent at 2 characters for the subsequent lines. It may also need line wrapping.

[billdenney]

For the names at the end where they're all capital letters, I think that will get push-back. Can you please make them into normal case for proper nouns?