fix props anchor links

Summary:All anchor links are broken because of https://github.com/facebook/react-native/blob/master/website/core/Site.js#L37 base tag it means that relative urls won't work.
closes #5450
proof
![screen shot 2016-02-29 at 13 34 35](https://cloud.githubusercontent.com/assets/1488195/13392082/3d14a00e-dee9-11e5-8611-bc6bfaf6c752.png)
Closes https://github.com/facebook/react-native/pull/6208

Differential Revision: D2988892

Pulled By: vjeux

fb-gh-sync-id: da8b621af92d792a258812e38ae15f7cf53873ca
shipit-source-id: da8b621af92d792a258812e38ae15f7cf53873ca

website/core/Header.js

@@ -13,6 +13,10 @@ var React = require('React');
 var slugify = require('slugify');
 
 var Header = React.createClass({
+  getDefaultProps: function() {
+    return {permalink: ''};
+  },
+
   render: function() {
     var slug = slugify(this.props.toSlug || this.props.children);
     var H = 'h' + this.props.level;
@@ -20,7 +24,7 @@ var Header = React.createClass({
       <H {...this.props}>
         <a className="anchor" name={slug}></a>
         {this.props.children}
-        {' '}<a className="hash-link" href={'#' + slug}>#</a>
+        {' '}<a className="hash-link" href={this.props.permalink + '#' + slug}>#</a>
       </H>
     );
   }

website/layout/AutodocsLayout.js

@@ -110,7 +110,7 @@ var ComponentDoc = React.createClass({
   renderProp: function(name, prop) {
     return (
       <div className="prop" key={name}>
-        <Header level={4} className="propTitle" toSlug={name}>
+        <Header level={4} className="propTitle" toSlug={name} permalink={this.props.permalink}>
           {prop.platforms && prop.platforms.map(platform =>
             <span className="platform">{platform}</span>
           )}
@@ -488,7 +488,7 @@ var Autodocs = React.createClass({
     var metadata = this.props.metadata;
     var docs = JSON.parse(this.props.children);
     var content  = docs.type === 'component' || docs.type === 'style' ?
-      <ComponentDoc content={docs} /> :
+      <ComponentDoc content={docs} permalink={metadata.permalink}/> :
       <APIDoc content={docs} apiName={metadata.title} />;
 
     return (