Reorganize directories (#3462)

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

docs/examples/update__range.cpp

@@ -0,0 +1,23 @@
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create two JSON objects
+    json o1 = R"( {"color": "red", "price": 17.99, "names": {"de": "Flugzeug"}} )"_json;
+    json o2 = R"( {"color": "blue", "speed": 100, "names": {"en": "plane"}} )"_json;
+    json o3 = o1;
+
+    // add all keys from o2 to o1 (updating "color", replacing "names")
+    o1.update(o2.begin(), o2.end());
+
+    // add all keys from o2 to o1 (updating "color", merging "names")
+    o3.update(o2.begin(), o2.end(), true);
+
+    // output updated object o1 and o3
+    std::cout << std::setw(2) << o1 << '\n';
+    std::cout << std::setw(2) << o3 << '\n';
+}