Reorganize directories (#3462)

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

docs/examples/push_back__object_t__value.cpp

@@ -0,0 +1,25 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create JSON values
+    json object = {{"one", 1}, {"two", 2}};
+    json null;
+
+    // print values
+    std::cout << object << '\n';
+    std::cout << null << '\n';
+
+    // add values
+    object.push_back(json::object_t::value_type("three", 3));
+    object += json::object_t::value_type("four", 4);
+    null += json::object_t::value_type("A", "a");
+    null += json::object_t::value_type("B", "b");
+
+    // print values
+    std::cout << object << '\n';
+    std::cout << null << '\n';
+}