Reorganize directories (#3462)

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

docs/examples/to_ubjson.cpp

@@ -0,0 +1,63 @@
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+// function to print UBJSON's diagnostic format
+void print_byte(uint8_t byte)
+{
+    if (32 < byte and byte < 128)
+    {
+        std::cout << (char)byte;
+    }
+    else
+    {
+        std::cout << (int)byte;
+    }
+}
+
+int main()
+{
+    // create a JSON value
+    json j = R"({"compact": true, "schema": false})"_json;
+
+    // serialize it to UBJSON
+    std::vector<std::uint8_t> v = json::to_ubjson(j);
+
+    // print the vector content
+    for (auto& byte : v)
+    {
+        print_byte(byte);
+    }
+    std::cout << std::endl;
+
+    // create an array of numbers
+    json array = {1, 2, 3, 4, 5, 6, 7, 8};
+
+    // serialize it to UBJSON using default representation
+    std::vector<std::uint8_t> v_array = json::to_ubjson(array);
+    // serialize it to UBJSON using size optimization
+    std::vector<std::uint8_t> v_array_size = json::to_ubjson(array, true);
+    // serialize it to UBJSON using type optimization
+    std::vector<std::uint8_t> v_array_size_and_type = json::to_ubjson(array, true, true);
+
+    // print the vector contents
+    for (auto& byte : v_array)
+    {
+        print_byte(byte);
+    }
+    std::cout << std::endl;
+
+    for (auto& byte : v_array_size)
+    {
+        print_byte(byte);
+    }
+    std::cout << std::endl;
+
+    for (auto& byte : v_array_size_and_type)
+    {
+        print_byte(byte);
+    }
+    std::cout << std::endl;
+}