Make doc index work with translated documentation too

1. Distinguish doc index using appropriate language-specific permalink.
   Fortunately, doc-heading.html already sets 'doc_link' variable.
2. For translated doc, iterate over site.translated, instead of
   site.doc.

Author: marmarek

_includes/doc-index.html

@@ -3,6 +3,7 @@
   {% assign doc_content = site.data.includes %}
   {% assign lang = "" %}
   {% assign indexed = site.data.doc-index %}
+  {% assign all_docs = site.doc  %}
 {% else %}
   {% assign lang = "/" | append: page.lang %}
   {% assign doc_content = site.data.translation[page.lang].includes %}
@@ -13,6 +14,7 @@
   {% if indexed == nil or indexed.size == 0 %}
     {% assign indexed = site.data.doc-index %}
   {% endif %}
+  {% assign all_docs = site.translated %}
 {% endif %}
 {% assign docs = doc_content | where_exp: "item", "item.section == 'doc-content'" | first %}
 <!-- Opening HTML for doc content -->
@@ -41,7 +43,7 @@ <h2 id="{{ item.title | downcase | replace: " ", "-" | replace: ",",""}}">{{ ite
       {% if item.category == 'external' %}
         <li><a href="{{ sub.url }}">{{ sub.text }}</a></li>
       {%- else %}
-        {% for page in site.doc %}{% if page.url == sub.url -%}
+        {% for page in all_docs %}{% if page.url == sub.url -%}
           <li><a href="{{ sub.url }}">{{ page.title }}</a></li>
         {%- endif  %}{% endfor %}
       {%- endif %}
@@ -64,7 +66,7 @@ <h3 id="{{ sub2.title | downcase | replace: " ", "-" | replace: ",","" }}">{{ su
           {% if item.category == 'external' %}
             <li><a href="{{ sub3.url }}">{{ sub3.text }}</a></li>
           {%- else %}
-           {% for page in site.doc -%}
+           {% for page in all_docs -%}
              {% if page.url == sub3.url -%}
                <li><a href="{{ sub3.url }}">{{ page.title }}</a></li>
              {%- endif %}

_layouts/doc.html

@@ -4,7 +4,7 @@
 <div class="container">
   {% include doc-heading.html %}
   <div class="more-bottom white-box page-content">
-    {% if page.permalink == '/doc/' %}
+    {% if page.permalink == doc_link %}
       {% include doc-index.html %}
     {% else %}
       {% include doc-content.html %}