Reorganize directories (#3462)

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

docs/examples/swap__array_t.cpp

@@ -0,0 +1,20 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON value
+    json value = {{"array", {1, 2, 3, 4}}};
+
+    // create an array_t
+    json::array_t array = {"Snap", "Crackle", "Pop"};
+
+    // swap the array stored in the JSON value
+    value["array"].swap(array);
+
+    // output the values
+    std::cout << "value = " << value << '\n';
+    std::cout << "array = " << array << '\n';
+}