Add support for loading older versioned save files.

[InsertCreativityHere]

While loading save files, we always check that the version baked into the file matches the current version of the program, and if it doesn't we throw an exception.

It's somewhat of a moot point right now, since there's only 1 version of the encoding it could possibly be, but in the future, support should be added for loading older save files and automatically converting them into a new format.