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/changelog.rst b/changelog.rst
index 94c68d8..8cc41c0 100644
--- a/changelog.rst
+++ b/changelog.rst
@@ -16,20 +16,24 @@
   + Move optional ``ForwardingHint`` element after ``MustBeFresh`` (before ``Nonce``)
   + Add optional ``HopLimit`` element
   + Add optional ``ApplicationParameters`` element
-  + Define a new specification for Signed Interest using new optional elements ``InterestSignatureInfo`` and ``InterestSignatureValue``
+  + Define a new specification for Signed Interest using two new elements: ``InterestSignatureInfo`` and ``InterestSignatureValue``
 
 - **Data**
 
   + Make ``MetaInfo`` and ``Content`` elements optional
-  + Change semantics of omitted (or set to zero) ``FreshnessPeriod`` element: it cannot be used to satisfy
-    Interests with ``MustBeFresh``
+  + Change semantics of omitted (or set to zero) ``FreshnessPeriod`` element: it cannot be used to satisfy Interests with ``MustBeFresh``
 
 - **Name**
 
-  + Lift restriction on name component types, allowing types in the range ``1`` - ``32767``.
-  + Correct definition of name URI encoding: disallow unescaped encoding of PLUS ``+`` and allow TILDE ``~``.
+  + Lift restriction on name component types, allowing types in the range ``1`` - ``32767``
+  + Correct definition of name URI encoding: disallow unescaped encoding of PLUS ``+`` and allow TILDE ``~``
   + Add ``ParametersSha256DigestComponent``
 
+- **Signature**
+
+  + Require all compliant implementations to support the ``SignatureSha256WithEcdsa`` signature type using NIST curve P-256
+  + Redefine the signed portion of Data packets to be more future-proof
+
 Version 0.2.1
 -------------
 
@@ -44,8 +48,6 @@
 
   + Updated Content Store semantics for Data packets that do not carry FreshnessPeriod.
 
-************************************************************
-
 Version 0.2
 -----------
 
@@ -71,8 +73,6 @@
 
   + Reserve 800-1000 range for link protocol
 
-************************************************************
-
 Version 0.1.1
 -------------
 
@@ -83,8 +83,6 @@
   + ``KeyLocator`` element is now defined to be optionally present in generic ``SignatureInfo`` element.
     ``SignatureSha256WithRsa`` and ``SignatureSha256WithEcdsa`` still require ``KeyLocator`` to be always present.
 
-************************************************************
-
 Version 0.1
 -----------