Add query parameters to state

[ghost]

Fixes #31

highway.route({
  name: 'home',
  path: '/',
  action (state) {
    console.log(state.query) // { hello: 'world' }
  }
})

// Navigate to http://<your-site>/?hello=world or
highway.go({ name: 'home', query: { hello: 'world' } })

• [x] Add section about query parameters to readme