Specify og:image for posts and individual pages (#1748)

This adds a larger, wide format version of the elixir log as the
og:image and twitter:image seo meta tags for all pages. Each layout and
non-post page must set the image separately to be included in the
rendered html.

_config.yml

@@ -26,3 +26,4 @@ defaults:
  values:
  layout: post
  permalink: /blog/:year/:month/:day/:title/
+ image: /images/social/elixir-og-card.jpg

cases.html

@@ -1,6 +1,7 @@
 ---
 section: cases
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 <h1>Cases</h1>

crash-course.markdown

@@ -2,6 +2,7 @@
 title: "Erlang/Elixir Syntax: A Crash Course"
 section: home
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 # {{ page.title }}

development.markdown

@@ -2,6 +2,7 @@
 title: "Development & Team"
 section: development
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 # {{ page.title }}

docs.markdown

@@ -2,6 +2,7 @@
 title: Elixir Documentation
 section: docs
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 # Documentation

index.html

@@ -1,6 +1,7 @@
 ---
 section: home
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 <div class="hfeed">

install.markdown

@@ -2,6 +2,7 @@
 title: "Installing Elixir"
 section: install
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 {% assign stable = site.data.elixir-versions[site.data.elixir-versions.stable] %}
 

learning.markdown

@@ -2,6 +2,7 @@
 title: "Learning resources"
 section: learning
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 # Learning

trademarks.markdown

@@ -2,6 +2,7 @@
 title: "Trademarks policy"
 section: trademarks
 layout: default
+image: /images/social/elixir-og-card.jpg
 ---
 
 # {{ page.title }}