A wrapper around a set of downloading functions

Currently, this only deals with drive_download, and download.file.

downloadFile(archive, targetFile, neededFiles, destinationPath, quick,
  checksumFile, checkSums, url, needChecksums, overwrite = TRUE,
  purge = FALSE)

Arguments

archive	Optional character string giving the path of an archive containing targetFile, or a vector giving a set of nested archives (e.g., c("xxx.tar", "inner.zip")). If there is/are (an) inner archive(s), but they are unknown, the function will try all until it finds the targetFile
targetFile	Character string giving the path to the eventual file (raster, shapefile, csv, etc.) after downloading and extracting from a zip or tar archive. This is the file before it is passed to postProcess. Currently, the internal checksumming does not checksum the file after it is postProcessed (e.g., cropped/reprojected/masked). Using Cache around prepInputs will do a sufficient job in these cases.
neededFiles	Character string giving the name of the file(s) to be extracted.
destinationPath	Character string of a directory in which to download and save the file that comes from url and is also where the function will look for archive or targetFile.
quick	Logical. This is passed internally to Checksums (the quickCheck argument), and to Cache (the quick argument). This results in faster, though less robust checking of inputs. See the respective functions.
checksumFile	A character string indicating the absolute path to the CHECKSUMS.txt file.
checkSums	A checksums file, e.g., created by Checksums(..., write = TRUE)
url	Optional character string indicating the URL to download from. Normally, if used within a module, this url should be explicitly given as sourceURL for an expectsInput. In that case, it will use the module's checksums file to confirm that the download occurred correctly. If URL is used here, an ad hoc checksums will be created in the destinationPath. This will be used in subsequent calls to prepInputs, comparing the file on hand with the ad hoc CHECKSUMS.txt.
needChecksums	A numeric, with 0 indicating do not write a new checksums, 1 write a new one, 2 append new information to existing one.
overwrite	Logical. Should downloading and all the other actions occur even if they pass the checksums or the files are all there.
purge	Logical or Integer. 0/FALSE (default) keeps existing CHECKSUMS.txt file and prepInputs will write or append to it. 1/TRUE will deleted the entire CHECKSUMS.txt file. Other options, see details.