Download the list of followers from your Mastodon account

The Problem It recently came to my mind that it might be handy to have a list of all the accounts that I follow on Mastodon. I can surely see them on the web or in any decent client, but as a backup it would be great to have a list to store somewhere. As I already played a little with the Mastodon API I decided to write a short script that downloads a list of user@instance values.