Reorganize directories (#3462)

* 🚚 move files
* 🚚 rename doc folder to docs
* 🚚 rename test folder to tests

docs/examples/json_pointer__operator_add_binary.cpp

@@ -0,0 +1,19 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON pointer
+    json::json_pointer ptr("/foo");
+
+    // append a JSON Pointer
+    std::cout << ptr / json::json_pointer("/bar/baz") << '\n';
+
+    // append a string
+    std::cout << ptr / "fob" << '\n';
+
+    // append an array index
+    std::cout << ptr / 42 << std::endl;
+}