Switch all GET requests to RETRY requests for robustness

[tanho63]

Is your feature request related to a problem? Please describe.
Suggestion for best-practice - RETRY is more robust to accidental API unavailability - per https://blog.r-hub.io/2020/04/07/retry-wheel/

Describe the solution you'd like
Should be as simple as swapping out all instances of httr::GET(...) with httr::RETRY("GET",...) - is drop-in replacement

[saiemgilani]

archiving repository, this suggestion was implemented in cfbfastR per suggestion.