feat: rewrite programming-challenges CLI (#3)

templates/solution/cpp/solution.cpp

@@ -0,0 +1,9 @@
+#include <iostream>
+#include <string>
+
+int main() {
+  for (std::string line; std::getline(std::cin, line);) {
+    std::cout << "Hello, " + line + "!" << std::endl;
+  }
+  return 0;
+}