Add a way to download a filing only if it hasn't already been downloaded

[bycoffe]

I think something like this has come up before -- whether Filing#download should re-download a filing if the file already exists.

While I still think it should assume the user wants to re-download the file when Filing#download is called, what if we added either:

• A parameter to Filing#download that told it to download the filing only if the file doesn't already exist.
• A new method on Filing (maybe Filing#download_if_needed) that would download the filing only if the file doesn't already exist.

I frequently use the pattern:

filing.download unless File.exists?(filing.file_path)

but making that check easier would be helpful in a lot of situations.

[dwillis]

I would go for adding an optional param to Filing#download.