docs+ndnsec: improve description and parsing of command options, rewrite man pages

Replace custom redmine_issue extension with sphinx.ext.extlinks

Refs: #4907
Change-Id: Ib0cb94156ae4fc80cdcaf4c70d7c8d55c16fcbc3
diff --git a/docs/manpages/ndnsec-set-default.rst b/docs/manpages/ndnsec-set-default.rst
index 4af6ad9..05c6677 100644
--- a/docs/manpages/ndnsec-set-default.rst
+++ b/docs/manpages/ndnsec-set-default.rst
@@ -1,49 +1,43 @@
 ndnsec-set-default
 ==================
 
-``ndnsec-set-default`` is a tool to change the default security settings.
+Synopsis
+--------
 
-Usage
------
-
-::
-
-    ndnsec-set-default [-h] [-k|c] name
+**ndnsec-set-default** [**-h**] [**-k**\|\ **-c**] *name*
 
 Description
 -----------
 
-By default, ``ndnsec-set-default`` takes ``name`` as an identity name and sets the identity as the
-system default identity.
+:program:`ndnsec-set-default` allows changing the default security settings.
+
+Without any options, *name*, which must be an identity name, is set as the
+default identity for the current user.
 
 Options
 -------
 
-``-k``
-  Set default key. ``name`` should be a key name, ``ndnsec-set-default`` can infer the corresponding
-  identity and set the key as the identity's default key.
+.. option:: -k, --default-key
 
-``-c``
-  Set default certificate. ``name`` should be a certificate name, ``ndnsec-set-default`` can
-  infer the corresponding key name and set the certificate as the key's default certificate.
+   Set *name*, which must be a key name, as the default key for the
+   corresponding identity.
 
-Examples
---------
+.. option:: -c, --default-cert
 
-Set a key's default certificate:
+   Set *name*, which must be a certificate name, as the default certificate
+   for the corresponding key.
 
-::
+Example
+-------
+
+Set a key's default certificate::
 
     $ ndnsec-set-default -c /ndn/test/KEY/alice/ksk-1394129695025/ID-CERT/%FD%01D%98%9A%F2%3F
 
-Set an identity's default key:
-
-::
+Set an identity's default key::
 
     $ ndnsec-set-default -k /ndn/test/alice/ksk-1394129695025
 
-Set system default identity:
-
-::
+Set the user's default identity::
 
     $ ndnsec-set-default /ndn/test/alice