Add option to override filename for download

[goodevilgenius]

It would be nice to be able to override the default filename when downloading a file.

I think it would just return an error if downloading more than one file and this option was set.

I don't mind having a go at implementing this myself and submitting a PR. I'll have a look sometime soon if that's a feature you'd be open to adding.

[jkawamoto]

Thank you for posting this issue.

I think your suggestion to override the default filename when downloading a file is a good idea. I am very grateful that you are willing to implement this feature, and I look forward to your PR.