add support for unique page titles

partly addresses #357 with updates needed to pages sitewide to use implement title: within the frontmatter for every page where it is currently missing

_config.yml

@@ -13,7 +13,7 @@
 # you will see them accessed via {{ site.title }}, {{ site.email }}, and so on.
 # You can create any custom variable you would like, and they will be accessible
 # in the templates via {{ site.myvariable }}.
-title: GSA Centers of Excellence
+title: GSA - IT Modernization Centers of Excellence
 email:  [email protected]
 description: >- # this means to ignore newlines until "baseurl:"
   The Centers of Excellence (CoE) are accelerating the modernization of IT 

_includes/header.html

@@ -21,7 +21,16 @@
   <meta name="msapplication-TileColor" content="#ffffff">
   <meta name="msapplication-TileImage" content="{{site.baseurl}}/icons/ms-icon-144x144.png">
   <meta name="theme-color" content="#ffffff">
-  <title>GSA - IT Modernization Centers of Excellence</title>
+  <!-- Title -->
+  {% if page.title %}
+    <title>{{ page.title }} | {{ site.title }}</title>
+    <meta property="og:title" content="{{ page.title | xml_escape }} | {{ site.title | xml_escape }}" />
+    <meta name="twitter:title" content="{{ page.title | xml_escape }} | {{ site.title | xml_escape }}">
+  {% else %}
+    <title>{{ site.title }} | {{ site.description }}</title>
+    <meta property="og:title" content="{{ site.title | xml_escape }} | {{ site.title | xml_escape }}" />
+    <meta property="twitter:title" content="{{ site.title | xml_escape }} | {{ site.title | xml_escape }}" />
+  {% endif %}
 
   {% assign description = page.description | default: site.description %}
   {% if description %}