Add RSS feed for blog posts

[j0k3r]

I needed React >= 0.14.0 to avoid self-closing tag (see facebook/react#2842) in RSS (mostly for the <link /> node).
Feel free to jump to any most up to date version below the 0.14.

I've also hacked around to be able to generate a xml file instead of html.

Content is not included in the RSS because I cannot find a way to sanitize the html. So the RSS wasn't valid. Most problem came from url with parameter in the html (like youtube link with a &).

Here is the RSS generated:

<?xml version="1.0" encoding="UTF-8"?>
<feed>
   <title>Blog | GraphQL</title>
   <link href="http://graphql.org/blog/" />
   <entry>
      <title>Wrapping a REST API in GraphQL</title>
      <link href="http://graphql.org/blog/rest-api-graphql-wrapper/" />
      <id>/blog/rest-api-graphql-wrapper/</id>
      <updated>2016-05-04T22:00:00.000Z</updated>
      <summary>Wrapping a REST API in GraphQL</summary>
      <content>Wrapping a REST API in GraphQL</content>
      <author>
         <name>Steven Luscher</name>
      </author>
   </entry>
   <entry>
      <title>Mocking your server is easy with GraphQL</title>
      <link href="http://graphql.org/blog/mocking-with-graphql/" />
      <id>/blog/mocking-with-graphql/</id>
      <updated>2016-04-18T22:00:00.000Z</updated>
      <summary>Mocking your server is easy with GraphQL</summary>
      <content>Mocking your server is easy with GraphQL</content>
      <author>
         <name>Jonas Helfer</name>
      </author>
   </entry>
   <entry>
      <title>Subscriptions in GraphQL and Relay</title>
      <link href="http://graphql.org/blog/subscriptions-in-graphql-and-relay/" />
      <id>/blog/subscriptions-in-graphql-and-relay/</id>
      <updated>2015-10-15T22:00:00.000Z</updated>
      <summary>Subscriptions in GraphQL and Relay</summary>
      <content>Subscriptions in GraphQL and Relay</content>
      <author>
         <name>Dan Schafer and Laney Kuenzel</name>
      </author>
   </entry>
   <entry>
      <title>GraphQL: A data query language</title>
      <link href="http://graphql.org/blog/graphql-a-query-language/" />
      <id>/blog/graphql-a-query-language/</id>
      <updated>2015-09-13T22:00:00.000Z</updated>
      <summary>GraphQL: A data query language</summary>
      <content>GraphQL: A data query language</content>
      <author>
         <name>Lee Byron</name>
      </author>
   </entry>
</feed>

It should fix #9

[ghost]

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[leebyron]

!!! This is so good!

[j0k3r]

@leebyron thanks :)