Different philosophy for rel prev/next links based on recommendations from Google.

Details here: https://webmasters.googleblog.com/2011/09/pagination-with-relnext-and-relprev.html.

This replaces the per-page prev/next links with general ones that will be output whenever there is a paginator with a previous or next page to show.

README.md

@@ -11,7 +11,7 @@ Jekyll SEO Tag adds the following meta tags to your site:
 * Pages title (with site title appended when available)
 * Page description
 * Canonical URL
-* Next and previous URLs for posts
+* Next and previous URLs on paginated pages
 * [JSON-LD Site and post metadata](https://developers.google.com/structured-data/) for richer indexing
 * [Open graph](http://ogp.me/) title, description, site title, and URL (for Facebook, LinkedIn, etc.)
 * [Twitter summary card](https://dev.twitter.com/cards/overview) metadata

lib/jekyll-seo-tag.rb

@@ -30,6 +30,7 @@ module Jekyll
       {
         'page'    => context.registers[:page],
         'site'    => context.registers[:site].site_payload['site'],
+        'paginator' => context['paginator'],
         'seo_tag' => options
       }
     end

lib/template.html

@@ -139,14 +139,13 @@
 {% if page.date %}
   <meta property="og:type" content="article" />
   <meta property="article:published_time" content="{{ page.date | date_to_xmlschema }}" />
+{% endif %}
 
-  {% if page.next.url %}
-    <link rel="next" href="{{ page.next.url | prepend: seo_url | replace:'/index.html','/' }}" title="{{ page.next.title | escape }}" />
-  {% endif %}
-
-  {% if page.previous.url %}
-    <link rel="prev" href="{{ page.previous.url | prepend: seo_url | replace:'/index.html','/' }}" title="{{ page.previous.title | escape }}" />
-  {% endif %}
+{% if paginator.previous_page %}
+  <link rel="prev" href="{{ paginator.previous_page_path | prepend: seo_url }}">
+{% endif %}
+{% if paginator.next_page %}
+  <link rel="next" href="{{ paginator.next_page_path | prepend: seo_url }}">
 {% endif %}
 
 {% if site.twitter %}