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/management/nfd-control-parameters.hpp b/src/management/nfd-control-parameters.hpp
index b546d5e..82c08ad 100644
--- a/src/management/nfd-control-parameters.hpp
+++ b/src/management/nfd-control-parameters.hpp
@@ -72,12 +72,12 @@
 class ControlParameters
 {
 public:
-  class Error : public Tlv::Error
+  class Error : public tlv::Error
   {
   public:
     explicit
     Error(const std::string& what)
-      : Tlv::Error(what)
+      : tlv::Error(what)
     {
     }
   };
@@ -471,7 +471,7 @@
   m_wire.parse();
   Block::element_const_iterator val;
 
-  val = m_wire.find(Tlv::Name);
+  val = m_wire.find(tlv::Name);
   m_hasFields[CONTROL_PARAMETER_NAME] = val != m_wire.elements_end();
   if (this->hasName()) {
     m_name.wireDecode(*val);