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/docs/doxygen.conf.in b/docs/doxygen.conf.in
index 2779491..d1ab057 100644
--- a/docs/doxygen.conf.in
+++ b/docs/doxygen.conf.in
@@ -1924,7 +1924,8 @@
                          PROTECTED_WITH_TESTS_ELSE_PRIVATE=private \
                          VIRTUAL_WITH_TESTS \
                          NDN_CXX_KEYCHAIN_REGISTER_PIB \
-                         NDN_CXX_KEYCHAIN_REGISTER_TPM
+                         NDN_CXX_KEYCHAIN_REGISTER_TPM \
+                         DEPRECATED(x)=x
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The