prep cran release

[shannonhaughton]

First release

• usethis::use_news_md()
• usethis::use_cran_comments()
• Update (aspirational) install instructions in README
• Proofread Title: and Description:
• Check that all exported functions have @returns and @examples
• Check that Authors@R: includes a copyright holder (role ‘cph’)
• Check licensing of included files
• Review https://github.com/DavisVaughan/extrachecks

[shannonhaughton]

run through cran release chapter of r packages book