A function to download all the CRN files
The function is passed a url for daily or hourly data, a matching directory, and sequence of years to download. The function will then download all the files and place them in the right directory.
Must be either CRN.DAILY.URL or CRN.HOURLY.URL
Must match the url: DAILY_DIR or HOURLY_DIR
a sequence of years to download. On initial download you should download all files. For updates just use the last year
The function iterates through the years in the sequence, fetches all the urls for the files in those subdirectories and downloads them all
Side effect is downloaded files
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