Better archiving format

[nickoneill]

I imagine the native plist serialization format is huge and clunky. It's fine for small things but to efficiently store larger struct objects, we'll probably have to consider a different format. I am not an expert here so I have no clue what this would look like at the moment.

A couple considerations though:

• It should still be able to unarchive a changed struct (throw away keys that don't exist or ignore keys that have no stored value)