Reorganize directories (#3462)

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

docs/examples/swap__object_t.cpp

@@ -0,0 +1,20 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON value
+    json value = { {"translation", {{"one", "eins"}, {"two", "zwei"}}} };
+
+    // create an object_t
+    json::object_t object = {{"cow", "Kuh"}, {"dog", "Hund"}};
+
+    // swap the object stored in the JSON value
+    value["translation"].swap(object);
+
+    // output the values
+    std::cout << "value = " << value << '\n';
+    std::cout << "object = " << object << '\n';
+}