Use a common main

lib/src/Startup.cpp

@@ -29,3 +29,13 @@ auto Startup(int argc, char ** argv) -> std::unique_ptr<std::istream, void(*)(st
 }
 
 }
+
+auto main(int argc, char ** argv) -> int
+{
+  try {
+    Main(*aocpp::Startup(argc, argv));
+  } catch (std::exception const& e) {
+    std::cerr << "Program failed: " << e.what() << std::endl;
+    return 1;
+  }
+}