Clean up and document project files (#4560)

docs/mkdocs/docs/examples/json_pointer__empty.cpp

@@ -0,0 +1,20 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // different JSON Pointers
+    json::json_pointer ptr0;
+    json::json_pointer ptr1("");
+    json::json_pointer ptr2("/foo");
+    json::json_pointer ptr3("/foo/0");
+
+    // call empty()
+    std::cout << std::boolalpha
+              << "\"" << ptr0 << "\": " << ptr0.empty() << '\n'
+              << "\"" << ptr1 << "\": " << ptr1.empty() << '\n'
+              << "\"" << ptr2 << "\": " << ptr2.empty() << '\n'
+              << "\"" << ptr3 << "\": " << ptr3.empty() << std::endl;
+}