p_archive opens in the browser one page per package and displays
the package versions stored in CRAN archive.
p_archive_lst prints in the console a list of the package versions
stored in CRAN archive.
l_targz takes as input the list issued by p_archive_lst
and lists the last package versions archived before a certain date.
Use p_downarch to download packages from the CRAN archives,
either the latest version stored or a specific version number.
Use archivedb_list to list all packages stored in CRAN archive
(does not include the valid packages having a single version which are stored
in regular CRAN).