Clean up and document project files (#4560)

docs/mkdocs/docs/examples/json_pointer__string_t.cpp

@@ -0,0 +1,13 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    json::json_pointer::string_t s = "This is a string.";
+
+    std::cout << s << std::endl;
+
+    std::cout << std::boolalpha << std::is_same<json::json_pointer::string_t, json::string_t>::value << std::endl;
+}