Added some std functions.

std/iterator.hpp

@@ -1,4 +1,6 @@
 #pragma once
 
 #include <iterator>
+
 using std::back_inserter;
+using std::distance;

std/map.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
 #include <map>
+#include <boost/unordered_map.hpp>
 
 using std::map;
+using boost::unordered_map;