List available releases
Lists all available releases (year.month format). To use a specific release, set the desired release using `options(FISHBASE_VERSION=)`, as shown in the examples. Otherwise, rfishbase will use the latest available version if this option is unset. NOTE: it will be necessary to clear the cache with `clear_cache()` or by restarting the R session with a fresh environment.
available_releases()#>  "19.04" "18.1" "18.07" "17.07"