* [@types/next] Update Router.push() method to include UrlLike type
Allow a valid UrlLike object instead of only a string type e.g
```
Router.push({
pathname: '/pathname',
query: {
prop1: '',
prop2: '',
},
});
```
https://github.com/zeit/next.js/#with-url-object-1
* Update router.d.ts
- Some of the `render` parameters should've been made optional.
- The export style of the `'next'` module wasn't correct.
- Added some missing static methods to `Head`
- Some readonly properties of `Router` can be `undefined`.
Note that this also means that `'next'` technically needs to be imported
like `import next = require('next');`
