Update, 5/17/2019
I am a little late to update this post, but it appears as though someone did submit a pull request back in November of 2018 with the fixes required to make the theme work with the newest version of Ghost. You can find the official repository of the Odin theme here.
So let me begin this by saying I've been pretty bad about checking for updates to Ghost, which is what powers this blog. I'm not consistent with actually logging into the administration panel which is where they would alert me to new versions. I also never check the Ghost site, as there really isn't much of a reason since I don't currently make themes so I wouldn't ever need to look at their site for any reason.
So imagine my surprise when I logged in and it alerted me that there was a new Ghost version available (version 2.something). This version introduced a new editor (which isn't all that bad, honestly), and also introduced a bunch of changes to theming.
As I began to work through the update it alerted me that the theme I was using wasn't compatible with 2.x as it was using older theme options which were deprecated in this new release. I knew right away that I would fix the theme, as I am a huge fan of it and wasn't going to spend time trying to find a 2.x theme I liked as much as this one.
I began by first visiting the Ghost website to grab the new CSS that was required for the new editor. This was pretty straight forward, I just had to visit the Casper theme on the Ghost GitHub to copy the CSS over. After this, it was just a matter of updating deprecated code to use the new syntax within the theme (e.g {author} becoming {primary_author}). While this was a time consuming process, it was totally worth it to keep my theme and even learn a bit about writing themes for Ghost, which is still something I want to do at some point in the future (I want my own custom theme for this blog).
While I haven't yet sent a pull request to the source repository on GitHub (I need to refork the source and make my changes, my repository isn't actually a fork of that right now but instead was cloned and a new repository created). For now, if you are interested in using this theme for your own Ghost blog, you can find the source here.