Reorganize directories (#3462)

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

docs/examples/operator_deserialize.cpp

@@ -0,0 +1,26 @@
+#include <iostream>
+#include <iomanip>
+#include <sstream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create stream with serialized JSON
+    std::stringstream ss;
+    ss << R"({
+        "number": 23,
+        "string": "Hello, world!",
+        "array": [1, 2, 3, 4, 5],
+        "boolean": false,
+        "null": null
+    })";
+
+    // create JSON value and read the serialization from the stream
+    json j;
+    ss >> j;
+
+    // serialize JSON
+    std::cout << std::setw(2) << j << '\n';
+}