Reorganize directories (#3462)

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

docs/examples/unflatten.cpp

@@ -0,0 +1,26 @@
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create JSON value
+    json j_flattened =
+    {
+        {"/answer/everything", 42},
+        {"/happy", true},
+        {"/list/0", 1},
+        {"/list/1", 0},
+        {"/list/2", 2},
+        {"/name", "Niels"},
+        {"/nothing", nullptr},
+        {"/object/currency", "USD"},
+        {"/object/value", 42.99},
+        {"/pi", 3.141}
+    };
+
+    // call unflatten()
+    std::cout << std::setw(4) << j_flattened.unflatten() << '\n';
+}