Added std functions.

std/algorithm.hpp

@@ -7,3 +7,4 @@ using std::min;
 using std::max;
 using std::transform;
 using std::equal_range;
+using std::replace;

std/fstream.hpp

@@ -0,0 +1,4 @@
+#pragma once
+
+#include <fstream>
+using std::ifstream;

std/string.hpp

@@ -3,3 +3,4 @@
 #include <string>
 
 using std::string;
+using std::getline;