Complete says that all of the bindings in this module can be accounted for internally or via `includes` (and maybe via `addsTo`, i forget). This implementation verifies downstream usage of the bindings that a module exposes.

Breaks complete:
```java
@Module class NotCompleteModule {
  @Provides Foo provideFoo(Bar bar) {
    return Foo.of(bar);
  }
}
```

Breaks this pull's check:
```java
@Module class UnusedModule {
  @Provides Foo provideFoo() {
    return new Foo();
  }
  @Provides Bar provideBar() {
    return new Bar();
  }
}
class App {
  @Inject Bar bar;
}
OG.create(new UnusedModule()).get(App.class);
```

Basically, if you `@Provide` something and don't use it anywhere.