Set <aside> as semantic sidebar element

Again, no effect on the visual presentation on the page. A purely
semantic improvement.

Author: karlstolley

_includes/sidebar-toc.html

@@ -5,7 +5,7 @@
 <input type="checkbox" class="sidebar-checkbox" id="sidebar-checkbox">
 
 <!-- Toggleable sidebar -->
-<div class="sidebar" id="sidebar">
+<aside class="sidebar" id="sidebar">
   <div class="sidebar-item">
     <p>{{ page.title }}</p>
   </div>
@@ -26,4 +26,4 @@
       Built with <a href="https://minicomp.github.io/ed/">Ed.</a> Distributed under an MIT license.
     </p>
   </div>
-</div>
+</aside>

_includes/sidebar.html

@@ -5,7 +5,7 @@
 <input type="checkbox" class="sidebar-checkbox" id="sidebar-checkbox">
 
 <!-- Toggleable sidebar -->
-<div class="sidebar" id="sidebar">
+<aside class="sidebar" id="sidebar">
   <div class="sidebar-item">
     <p>{{ site.description }}</p>
   </div>
@@ -45,4 +45,4 @@
       Built with <a href="https://minicomp.github.io/ed/">Ed.</a> Distributed under an MIT license.
     </p>
   </div>
-</div>
+</aside>