signature: redefine signed portion and make ECDSA P-256 mandatory

Also in this commit:
 - various cleanups and grammar fixes
 - unify RFC reference syntax on signature page
 - fix typo on tlv page
 - fix browser 'mixed content' warning

Refs: #4586, #5033
Change-Id: Iac7a54ad9a6863fda5c5428055a6256e9e086187
diff --git a/named_data_theme/layout.html b/named_data_theme/layout.html
index 8e1de4c..ec27157 100644
--- a/named_data_theme/layout.html
+++ b/named_data_theme/layout.html
@@ -12,7 +12,7 @@
         <div class="row">
              <div class="three columns">
                   <div id="logo">
-                        <a href="http://named-data.net" title="A Future Internet Architecture"><img src="http://named-data.net/wp-content/uploads/cropped-20130722_Logo2.png" alt="" /></a>
+                        <a href="https://named-data.net" title="A Future Internet Architecture"><img src="https://named-data.net/wp-content/uploads/cropped-20130722_Logo2.png" alt="" /></a>
                   </div><!--logo end-->
              </div>
 
@@ -70,7 +70,7 @@
         <div class="row">
             <div class="twelve columns">
 
-                <div id="copyright">This research is partially supported by NSF (Award <a href="http://www.nsf.gov/awardsearch/showAward?AWD_ID=1040868" target="_blank>">CNS-1040868</a>)<br/><br/><a rel="license" href="http://creativecommons.org/licenses/by/3.0/deed.en_US" target="_blank">Creative Commons Attribution 3.0 Unported License</a> except where noted.</div>
+                <div id="copyright">This research is partially supported by NSF (Award <a href="http://www.nsf.gov/awardsearch/showAward?AWD_ID=1040868" target="_blank>">CNS-1040868</a>)<br/><br/><a rel="license" href="https://creativecommons.org/licenses/by/3.0/deed.en_US" target="_blank">Creative Commons Attribution 3.0 Unported License</a> except where noted.</div>
 
             </div>
         </div>