CRAN version 0.6

New features:

• Update data import. New Unpaywall data fields include oa_status, has_repository_copy, journal_issns_l and published_date

Minor fixes:

• support new tidyr::unnest() interface introduced in version 1.0.0
• store email in .Renviron instead of .Rprofile
• bug fix RStudio addin
• build data frames with tibble::tibble
• improved tests and test coverage