Provision zipped data download

[zkamvar]

I've noticed an anti-pattern in one of the lessons in the incubator. The author of this lesson wants to distribute a 121k zip file that contains compressed content of the raw/ folder.

I think a nice utility that we could provide would be to have the user link the folder and then provision the zip file from that folder if they add an attribute to it like:

You can download the [zip archive of the raw data](../episodes/data/raw/){.zip}

We could then check for that in the setup, generate the zip archive on build time, and then replace the link in the rendered site.