[wwwdocs] Adjust (heading) levels of GCC 6 releases in the release notes

[Gerald Pfeifer]

After applying the change to document removal of the pcommit instruction
with GCC 6.3, I noticed the levels of headings were inconsistent, that is,
subheadings had the same level (<h2>) as their parent.

In the past we did not run into this since we usually did not have much
to document for minor releases.  

My recommendation, implemented and applied with the patch below, is to
use <h1> for minor releases as we do for the first heading on the page.
That allows us to keep any children at the same level.

Gerald

Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
retrieving revision 1.94
diff -u -r1.94 changes.html
--- changes.html        25 Feb 2017 17:10:32 -0000      1.94
+++ changes.html        25 Feb 2017 17:40:45 -0000
@@ -835,9 +835,6 @@
    in 32-bit mode whenever the use of SSE instructions is requested.</li>
   </ul>
 
-<!-- .................................................................. -->
-<!-- <h2>Documentation improvements</h2> -->
-
 
 <!-- .................................................................. -->
 <h2>Other significant improvements</h2>
@@ -853,7 +850,8 @@
        generation of PIE by default.</li>
   </ul>
 
-<h2><a name="6.2">GCC 6.2</a></h2>
+<!-- .................................................................. -->
+<h1><a name="6.2">GCC 6.2</a></h1>
 
 <p>This is the <a 
href="https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=6.2";>list
 of problem reports (PRs)</a> from GCC's bug tracking system that are
@@ -871,7 +869,7 @@
     <li>Support for the VIS 4.0 instruction set has been added.</li>
   </ul>
 
-<h2><a name="6.3">GCC 6.3</a></h2>
+<h1><a name="6.3">GCC 6.3</a></h1>
 
 <p>This is the <a 
href="https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&amp;resolution=FIXED&amp;target_milestone=6.3";>list
 of problem reports (PRs)</a> from GCC's bug tracking system that are
@@ -888,6 +886,5 @@
     pcommit instruction</a> has been removed.</li>
   </ul>
  
- <!-- ==================================================================== -->
 </body>
 </html>