Use "static" instead of "object" for PHPStorm autocomplete support.

I was recently working with this class when I discovered PHPStorm wasn't showing autocomplete for anything after the `getInstance` call on any class that used the singleton classes. As it was very annoying, I set out to fix it. It turns out, PHPStorm supports the "static" object type, representing an instance of the current class as one might expect.

I merely updated the PHPDoc blocks to use static instead of object so that autocomplete will be better supported.