feat: rewrite programming-challenges CLI (#3)

challenges/hello-world/solutions/cpp/function/README.md

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+# hello-world/cpp/function
+
+Created by [@Divlo](https://github.com/Divlo) on 7 June 2021.

challenges/hello-world/solutions/cpp/function/solution.cpp

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+#include <iostream>
+#include <string>
+
+int main() {
+  for (std::string line; std::getline(std::cin, line);) {
+    std::cout << "Hello, " + line + "!" << std::endl;
+  }
+  return 0;
+}