Reorganize directories (#3462)

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

docs/examples/operatorjson_pointer.cpp

@@ -0,0 +1,48 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON value
+    json j =
+    {
+        {"number", 1}, {"string", "foo"}, {"array", {1, 2}}
+    };
+
+    // read-only access
+
+    // output element with JSON pointer "/number"
+    std::cout << j["/number"_json_pointer] << '\n';
+    // output element with JSON pointer "/string"
+    std::cout << j["/string"_json_pointer] << '\n';
+    // output element with JSON pointer "/array"
+    std::cout << j["/array"_json_pointer] << '\n';
+    // output element with JSON pointer "/array/1"
+    std::cout << j["/array/1"_json_pointer] << '\n';
+
+    // writing access
+
+    // change the string
+    j["/string"_json_pointer] = "bar";
+    // output the changed string
+    std::cout << j["string"] << '\n';
+
+    // "change" a nonexisting object entry
+    j["/boolean"_json_pointer] = true;
+    // output the changed object
+    std::cout << j << '\n';
+
+    // change an array element
+    j["/array/1"_json_pointer] = 21;
+    // "change" an array element with nonexisting index
+    j["/array/4"_json_pointer] = 44;
+    // output the changed array
+    std::cout << j["array"] << '\n';
+
+    // "change" the array element past the end
+    j["/array/-"_json_pointer] = 55;
+    // output the changed array
+    std::cout << j["array"] << '\n';
+}