It's better that Counter behave not only `increment (add)` but also `decrement` or `reset`.
* Add decrement, reset handlers and rename add handler in `components/counter.js`
* Add increment, decrement, reset actions to `store.js`
* Rename page component class name: Counter => Index in `pages/index.js`
* Remove needless dispatch count event on getInitialProps in `pages/index.js`
* Format JSX to be readable in `pages/_app.js`
* Remove needless line from `components/examples.js`
* Remove needless spaces in `lib/with-redux-store.js`