add new topbar, improve the look & feel of web pages

Thank you, @chris-sab, for your excellent work and for helping us
commit this alpha version of the topbar.

As part of this work, the following HTML sections were removed:

* begin-row
* begin-leftcolumn
* sidenav
* end-leftcolumn
* begin-rightcolumn
* before-content
* end-rightcolumn
* end-row.default

Also added a new HTML section, just above the "header" section:

* topbar

The web site now as a more modern looking topbar, thanks to the
work of the contractor (GitHub user @chris-sab) who is working on
issue #2273.

Performed `make www` to implement the above and test under macOS.

TODO: Fix the Responsive Web Design to deal with
      the new topbar system.

TODO: Improve the topbar.  What is there now is
      just an alpha version.

TODO: Decide what to do with `png/ioccc.png`.
      Remove it make selective use of the image on certain top level
      pages lower down?

TODO: The changes to `ioccc.css` causes some
      formatting problems with pages such as `location.html` (missing
      blank lines).  Fix formatting problems as needed.

TODO: Fix the "Nu HTML check this web page"
      links on things like the year level _YYYY/index.html_ pages.

TODO: Correct all HTML errors, warnings and perhaps
      informative messages from the Nu HTML check.

TODO: Consider adding color (colour) to the
      web pages in such a way that people with color perception
      challenges can still use the web site.

TODO: For those web browsers that have and allow
      JavaScript, make use of technology such as [Code
      Mirror](https://codemirror.net/) to directly render source
      code (C, shell, Makefile, etc.) with syntax coloring (colouring)
      directly in the browser.  For non-JavaScript browsers, fallback
      to the current use of GitHub source code viewing.

inc/topbar.default.html

@@ -1,3 +1,67 @@
 <!-- START: this line starts content from: inc/topbar.default.html -->
 
+<div class="theader">
+  <nav class="topbar">
+    <div class="container">
+      <div class="logo">
+        IOCCC
+      </div>
+
+      <div class="topbar-items">
+        <div class="item">
+          <span class="item-header">
+            Home
+          </span>
+
+          <div class="sub-item">
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%index.html">IOCCC Home</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%years.html">Winning Entries</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%authors.html">People who have won</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%location.html">Location of authors</a></div>
+          </div>
+        </div>
+
+        <div class="item">
+          <span class="item-header">
+            News
+          </span>
+
+          <div class="sub-item">
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%news.html">IOCCC News</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%status.html">Contest status</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%next/index.html">Rules and Guidelines</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%faq.html#submit">How to enter the IOCCC</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%faq.html">FAQ</a></div>
+          </div>
+        </div>
+
+        <div class="item">
+          <span class="item-header">
+            Bugs
+          </span>
+
+          <div class="sub-item">
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%bugs.html">Bugs &amp; (mis)features</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%faq.html#fix_an_entry">Fixing IOCCC entries</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%faq.html#fix_web_site">Fixing the web site</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%faq.html#fix_author">Fixing author info</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%thanks-for-help.html">Thanks for the help</a></div>
+          </div>
+        </div>
+
+        <div class="item">
+          <span class="item-header">
+            Judges
+          </span>
+
+          <div class="sub-item">
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%judges.html">The IOCCC Judges</a></div>
+            <div class="outfit-font"><a href="%%DOCROOT_SLASH%%contact.html">Contacting the IOCCC</a></div>
+          </div>
+        </div>
+      </div>
+    </div>
+  </nav>
+</div>
+
 <!-- END: this line ends content from: inc/topbar.default.html -->