security: Reorganizing source code to prepare for support of two version of NDN certificates

This commit also removes unused ndn_digestSha256 function and deprecates
crypto::sha256 in favor of crypto::computeSha256Digest in util/crypto.hpp.

Change-Id: I24ee50ff073a96b868633bdf2cfade412d3605f3
Refs: #3098
diff --git a/src/security/sec-tpm-osx.hpp b/src/security/sec-tpm-osx.hpp
index 5ed93d5..1713f06 100644
--- a/src/security/sec-tpm-osx.hpp
+++ b/src/security/sec-tpm-osx.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2015 Regents of the University of California.
+ * Copyright (c) 2013-2016 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -33,6 +33,7 @@
 #include "sec-tpm.hpp"
 
 namespace ndn {
+namespace security {
 
 class SecTpmOsx : public SecTpm
 {
@@ -84,7 +85,7 @@
     deleteKeyPairInTpmInternal(keyName, false);
   }
 
-  virtual shared_ptr<PublicKey>
+  virtual shared_ptr<v1::PublicKey>
   getPublicKeyFromTpm(const Name& keyName);
 
   virtual Block
@@ -160,6 +161,10 @@
   shared_ptr<Impl> m_impl;
 };
 
+} // namespace security
+
+using security::SecTpmOsx;
+
 } // namespace ndn
 
 #endif // NDN_SECURITY_SEC_TPM_OSX_HPP