Export conversion script

This is the script for converting between version 0 and version 1 format.

I decided to not require a version number when calling the script-- instead, I determine which version the input arg is and convert to the opposite. If/when we get beyond version 1, we could change this script to require the desired version as an input arg.

I'm also not worrying about overwriting an existing tar.gz file with the same name as the converted one. Do you guys think I should throw an error if a file with that name already exists?

I introduced variables for "drafts" and "published". In the future, we will want to move the location of these variables and clean up all the places in our code where we hard-coded "draft" for the draft branch (note that I'm now using "drafts" because it was our existing folder name in version 0, and I didn't want to change it). I didn't think it was necessary to do that cleanup as part of this story.

@dmitchell @singingwolfboy Please review.