Add public API to determine if an object is an aphrodite style or not

I'm working on some components that have a `style` prop that's similar to the `style` prop in React Native components which can take either inline styles or styles from StyleSheet objects. The components need to know how to disambiguate between the types of objects being passed in so that they can apply the slides correctly in the render method.

Proposed API:
```
function isAphroditeStyle(style: any) => boolean
```

No file, test, or entry point is named. Start by locating the existing style-object handling and public exports, then determine where the proposed isAphroditeStyle API belongs; done means callers can distinguish inline styles from StyleSheet objects through that public function.

Written by the indexing model from the issue text.