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/name.hpp b/src/name.hpp
index 7522a19..0e8c840 100644
--- a/src/name.hpp
+++ b/src/name.hpp
@@ -77,7 +77,7 @@
    * Create a new Name with no components.
    */
   Name()
-    : m_nameBlock(Tlv::Name)
+    : m_nameBlock(tlv::Name)
   {
   }
 
@@ -198,10 +198,10 @@
   Name&
   append(const Block& value)
   {
-    if (value.type() == Tlv::NameComponent)
+    if (value.type() == tlv::NameComponent)
       m_nameBlock.push_back(value);
     else
-      m_nameBlock.push_back(Block(Tlv::NameComponent, value));
+      m_nameBlock.push_back(Block(tlv::NameComponent, value));
 
     return *this;
   }
@@ -220,7 +220,7 @@
   void
   clear()
   {
-    m_nameBlock = Block(Tlv::Name);
+    m_nameBlock = Block(tlv::Name);
   }
 
   /**
@@ -752,7 +752,7 @@
     }
 
   totalLength += blk.prependVarNumber(totalLength);
-  totalLength += blk.prependVarNumber(Tlv::Name);
+  totalLength += blk.prependVarNumber(tlv::Name);
   return totalLength;
 }
 
@@ -777,8 +777,8 @@
 inline void
 Name::wireDecode(const Block& wire)
 {
-  if (wire.type() != Tlv::Name)
-    throw Tlv::Error("Unexpected TLV type when decoding Name");
+  if (wire.type() != tlv::Name)
+    throw tlv::Error("Unexpected TLV type when decoding Name");
 
   m_nameBlock = wire;
   m_nameBlock.parse();