Add support for next page to use nextein/link to load a page with posts.

[Masse Fierro]

Use case:
Have an index page that renders a next page. Include a nextein/link to a blog page with a list of posts.

pages/index.js

import React form 'react'
import Link from 'nextein/link'

export default () => (
  <div>
    <h1>Hello There</h1>
    <p>This is a very simple component. With a link to <Link href="/blog"><a>My Blog</a></Link></p>
  </div>
)

pages/blog.js

import React from 'react'
import withPosts from 'nextein/posts'
import { Content } from 'nextein/post'

export default withPosts(({ posts }) => {
  return (
    <main>
    {
      posts.map((post, index) => (        
        <article key={`post-${index}`}>
          <h1>{post.data.title}</h1>
          <Content {...post} />
        </article>
      ))
    }
    </main>
  )
})