Add files

_includes/favicon.html

@@ -0,0 +1,23 @@
+{%- comment -%}
+  Include as: {%- include_cached favicon.html -%}
+  Depends on: site.static_files.
+  Results in: HTML for a link to an existing `favicon.ico` file.
+  Overwrites: 
+    file.
+  
+  The endoflife.date site has 226 pages and 3410 static files. @marcwrobel pointed
+  out that the time taken by evaluating the code in this file on every page when
+  building that site was significant, and suggested making it optional. As it is
+  page-independent, it can easily be cached. Doing that reduced the time taken by
+  rendering `_includes/head.html` from 15.294s to 10.760s, thereby reducing the
+  total build time from 26.074s to 21.656s -- a saving of about 17%.
+{%- endcomment -%}
+
+{% for file in site.static_files %}
+  {% if file.path == site.favicon_ico or file.path == '/favicon.ico' %}
+    {% assign favicon = true %}
+  {% endif %}
+{% endfor %}
+{% if favicon %}
+  <link rel="icon" href="{{ site.favicon_ico | default: '/favicon.ico' | relative_url }}" type="image/x-icon">
+{% endif %}