Refactor and modernize namespace declarations

Move all unit tests to namespace nfd::tests

Delete unused header core/algorithm.hpp

Change-Id: I5591f0c5f3bb5db67f8b45fae95471f8a555ca68
diff --git a/daemon/table/pit-iterator.hpp b/daemon/table/pit-iterator.hpp
index b788e3c..014ddc1 100644
--- a/daemon/table/pit-iterator.hpp
+++ b/daemon/table/pit-iterator.hpp
@@ -29,8 +29,7 @@
 #include "name-tree.hpp"
 #include "pit-entry.hpp"
 
-namespace nfd {
-namespace pit {
+namespace nfd::pit {
 
 /** \brief PIT iterator
  */
@@ -87,7 +86,6 @@
   size_t m_iPitEntry; ///< current PIT entry within m_ntIt->getPitEntries()
 };
 
-} // namespace pit
-} // namespace nfd
+} // namespace nfd::pit
 
 #endif // NFD_DAEMON_TABLE_PIT_ITERATOR_HPP