add config support

includes/tomlc17-R260618/README_CXX.md

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+# C++20 Accessors in tomlc17
+
+The library includes C++ class and routines in the `toml` namespace. These constructs provide:
+
+- **Safe resource management** - Result class respects RAII rules.
+- **Direct subtable access** – Retrieves values from nested subtables directly.
+- **Safe value access** – Uses C++ `std::optional` for error handling, throwing exceptions on invalid access.
+- **Time and date support** – Represents timestamps as `std::chrono` objects for precise time handling.
+- **Array conversion** – Converts datum arrays into integer or string vectors for easy manipulation.
+
+## Usage
+
+Here is a simple example:
+
+```c++
+/*
+ * Parse the config file simple.toml:
+ *
+ * [server]
+ * host = "www.example.com"
+ * port = [8080, 8181, 8282]
+ *
+ */
+#include "../src/tomlcpp.hpp"
+#include <iostream>
+#include <vector>
+
+using std::cout;
+
+static void error(const char *msg) {
+  fprintf(stderr, "ERROR: %s\n", msg);
+  exit(1);
+}
+
+int main() {
+  // Parse the toml file
+  toml::Result result = toml::parse_file_ex("simple.toml");
+
+  // Check for parse error
+  if (!result.ok()) {
+    error(result.errmsg());
+  }
+
+  // Extract values
+  std::string host;
+  std::vector<int64_t> port;
+
+  try {
+    // use the Datum::get() method
+    host = result.get({"server", "host"})->as_str().value();
+  } catch (const std::bad_optional_access &ex) {
+    error("missing or invalid 'server.host' property in config");
+  }
+
+  try {
+    // use the Datum::seek() method
+    port = result.seek("server.port")->as_intvec().value();
+  } catch (const std::bad_optional_access &ex) {
+    error("missing or invalid 'server.port' property in config");
+  }
+
+  // Print values
+  cout << "server.host = " << host << "\n";
+  cout << "server.port = [";
+  for (size_t i = 0; i < port.size(); i++) {
+    cout << (i ? ", " : "") << port[i];
+  }
+  cout << "]\n";
+
+  // Done! No need to call toml_free(). Result::~Result() will handle destruction.
+  return 0;
+}
+```