Addition: update figure role allowances

closes #412

As discussed in w3c/dpub-aria#42 (comment), `doc-example` is a dpub variant of the `figure` role.  This role being the same as `figure` but with the opportunity of being exposed as an "example" for its role description, needs to be an allowed role for the `figure` element.

index.html

@@ -1087,10 +1087,11 @@ <h2 id="docconformance">
                 <br>
                 <a><strong>Any `role`</strong></a>
               </p>
-              <p>
+              <p class="addition proposal">
                 If the `figure` has a `figcaption` descendant:
                 <br>
-                <a><strong class="nosupport">No `role`</strong></a>
+                DPub Role:
+                <a data-cite="dpub-aria-1.0#doc-example">`doc-example`</a>
               </p>
               <p>
                 <a data-cite="wai-aria-1.2#global_states">Global `aria-*` attributes</a> 
@@ -1121,7 +1122,7 @@ <h2 id="docconformance">
                 or <a href="#index-aria-none">`none`</a>
               </p>
               <p>
-                DPub Role:
+                DPub Role:doc-example
                 <a data-cite="dpub-aria-1.0#doc-footnote">`doc-footnote`</a>
               </p>
               <p class="proposed addition"><a>Naming Prohibited</a> if exposed as `generic`.</p>