define the destiny of archive.R

[espinielli]

archive.R deals with reading multinple FR24 flight files.

It has the benefit of dealing with the old problem reported to FR24 whereby CALLSIGN fields contained NULL characters (character string terminator \0) making the parsing of the filed fail by the underlying C library.

Ignoring this, multiple file read can simply be achieved with purrr (which is by the way used in import_flights_csvs too)