all: rename Tlv namespace to tlv for consistency

This commit renames the Tlv namespace defined in
tlv.hpp to tlv to be more consistent with tlv::security
and tlv::nfd. A Tlv namespace alias is provided for
backwards compatibility.

Change-Id: I21278d6a077afe7776802c3296997d4c1c44c6c6
diff --git a/src/security/sec-tpm-file.cpp b/src/security/sec-tpm-file.cpp
index 03ce634..7d0748d 100644
--- a/src/security/sec-tpm-file.cpp
+++ b/src/security/sec-tpm-file.cpp
@@ -332,7 +332,7 @@
                                  true,
                                  new SignerFilter(rng, signer, new FileSink(os)));
 
-                    return Block(Tlv::SignatureValue, os.buf());
+                    return Block(tlv::SignatureValue, os.buf());
                   }
                 default:
                   throw Error("Unsupported digest algorithm!");
@@ -368,7 +368,7 @@
 
                   shared_ptr<Buffer> sigBuffer = make_shared<Buffer>(buf, bufSize);
 
-                  return Block(Tlv::SignatureValue, sigBuffer);
+                  return Block(tlv::SignatureValue, sigBuffer);
                 }
               default:
                 throw Error("Unsupported digest algorithm!");