Feed file download example

[malwarefrank]

The current example only prints the sha256 of each file in the feed, see example/feed.go. It would help if that example also shows how to access the download_url and download the file, like the vt-py example.

[malwarefrank]

This may require a change to the vt-go package. The exposed functions, like Get and GetData, appear to assume a JSON response.

The simplest fix may be to add sendRequest to that list, as it does not parse the response.