* I didn't really understand NSProxy
But I think I do now :)
Previously I inherited from NSObject because I didn't think I needed
anything fancy, but it turns out NSProxy is *less* fancy than NSObject
and allows for overriding more methods. This change is probably purely
academic in that we don't use this class to forward NSObject specific
messages, but I believe this is the 'right thing'.
* Update comment, thanks @maicki!