Reorganize directories (#3462)

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

docs/examples/std_swap.cpp

@@ -0,0 +1,19 @@
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create JSON values
+    json j1 = {{"one", 1}, {"two", 2}};
+    json j2 = {1, 2, 4, 8, 16};
+
+    std::cout << "j1 = " << j1 << " | j2 = " << j2 << '\n';
+
+    // swap values
+    std::swap(j1, j2);
+
+    std::cout << "j1 = " << j1 << " | j2 = " << j2 << std::endl;
+}