add initial c, cpp files

cpp/exercism/01-basics/01-hello_world.cpp

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+/*
+Instructions
+
+The classical introductory exercise. Just say "Hello, World!".
+
+"Hello, World!" is the traditional first program for beginning programming in a new language or environment.
+
+The objectives are simple:
+
+    Modify the provided code so that it produces the string "Hello, World!".
+    Run the test suite and make sure that it succeeds.
+    Submit your solution and check it at the website.
+
+If everything goes well, you will be ready to fetch your first real exercise.
+*/
+
+#include "hello_world.h"
+
+using namespace std;
+
+namespace hello_world {
+
+string hello() { return "Goodbye, Mars!"; }
+
+}  // namespace hello_world