Reorganize directories (#3462)

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

docs/examples/operator__equal__nullptr_t.cpp

@@ -0,0 +1,22 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create several JSON values
+    json array = {1, 2, 3};
+    json object = {{"A", "a"}, {"B", "b"}};
+    json number = 17;
+    json string = "foo";
+    json null;
+
+    // output values and comparisons
+    std::cout << std::boolalpha;
+    std::cout << array << " == nullptr " << (array == nullptr) << '\n';
+    std::cout << object << " == nullptr " << (object == nullptr) << '\n';
+    std::cout << number << " == nullptr " << (number == nullptr) << '\n';
+    std::cout << string << " == nullptr " << (string == nullptr) << '\n';
+    std::cout << null << " == nullptr " << (null == nullptr) << '\n';
+}