Reorganize directories (#3462)

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

docs/examples/basic_json__basic_json.cpp

@@ -0,0 +1,17 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON array
+    json j1 = {"one", "two", 3, 4.5, false};
+
+    // create a copy
+    json j2(j1);
+
+    // serialize the JSON array
+    std::cout << j1 << " = " << j2 << '\n';
+    std::cout << std::boolalpha << (j1 == j2) << '\n';
+}