Improve implementation draft list layout

This adds a comma between `draft` and `date-draft` items and moves the
leading "draft-" text to before the first item.

Author: davishmcclurg

implementations.md

@@ -50,12 +50,14 @@ Validators
         <a href="{{ implementation.url}}">{{ implementation.name }}</a>
         <ul>
           <li><em>Supports:</em>
-            {% if implementation.date-draft %}
-                {{ implementation.date-draft | sort | reverse | join: ", " }}
-            {% endif %}
-            {% if implementation.draft %}
-                draft-0{{ implementation.draft | sort | reverse | join: ", -0" }}
-            {% endif %}
+            draft
+            {%- if implementation.date-draft and implementation.date-draft != empty -%}
+                -{{ implementation.date-draft | sort | reverse | join: ", " -}}
+                {%- if implementation.draft and implementation.draft != empty -%}, {% endif -%}
+            {%- endif -%}
+            {%- if implementation.draft and implementation.draft != empty -%}
+                -0{{ implementation.draft | sort | reverse | join: ", -0" -}}
+            {%- endif -%}
           </li>
 
         {% if implementation.compliance %}