I was hoping to be able to read through changes in this file without having to look at `SPDictionaryStorage` internals. But while reading, it wasn't clear your class was persisting everything automatically.

The "wrapping" of NSDictionary by using the exact same method names ends up feeling kind of strange, in my opinion.

Is there a way to make the persistence behavior more explicit? Maybe `setObject:forKey:persist:`? Or if persistence is mandatory, bake "persist" somewhere into the method name? `persistObject:forKey:`?