Proposing use of C++ header files and functions (#4869)

* Proposing use of C++ header files and functions 

Proposing use of C++ header files and functions instead of C header file and functions. 
Here are few examples for comparison : 

C                            C++
<cstdio>                <iostream> & <fstream>
printf()                     cout 
fopen()                    ifstream
etc ...

Please let me know if there are any comments.

* Updated diff based on review comments

docs/source/CppUsage.md

@@ -59,15 +59,18 @@ a `char *` array, which you pass to `GetMonster()`.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
     #include "flatbuffers/flatbuffers.h"
     #include "monster_test_generate.h"
-    #include <cstdio> // For printing and file access.
+    #include <iostream> // C++ header file for printing
+    #include <fstream> // C++ header file for file access
 
-    FILE* file = fopen("monsterdata_test.mon", "rb");
-    fseek(file, 0L, SEEK_END);
-    int length = ftell(file);
-    fseek(file, 0L, SEEK_SET);
+
+    std::ifstream infile;
+    infile.open("monsterdata_test.mon", std::ios::binary | std::ios::in);
+    infile.seekg(0,std::ios::end);
+    int length = infile.tellg();
+    infile.seekg(0,std::ios::beg);
     char *data = new char[length];
-    fread(data, sizeof(char), length, file);
-    fclose(file);
+    infile.read(data, length);
+    infile.close();
 
     auto monster = GetMonster(data);
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -78,9 +81,9 @@ If you look in your generated header, you'll see it has
 convenient accessors for all fields, e.g. `hp()`, `mana()`, etc:
 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
-    printf("%d\n", monster->hp());            // `80`
-    printf("%d\n", monster->mana());          // default value of `150`
-    printf("%s\n", monster->name()->c_str()); // "MyMonster"
+    std::cout << "hp : " << monster->hp() << std::endl;            // `80`
+    std::cout << "mana : " << monster->mana() << std::endl;        // default value of `150`
+    std::cout << "name : " << monster->name()->c_str() << std::endl;        // "MyMonster"
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 *Note: That we never stored a `mana` value, so it will return the default.*