Reorganize directories (#3462)

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

docs/examples/json_pointer__parent_pointer.cpp

@@ -0,0 +1,18 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // different JSON Pointers
+    json::json_pointer ptr1("");
+    json::json_pointer ptr2("/foo");
+    json::json_pointer ptr3("/foo/0");
+
+    // call parent_pointer()
+    std::cout << std::boolalpha
+              << "parent of " << ptr1 << " is " << ptr1.parent_pointer() << '\n'
+              << "parent of " << ptr2 << " is " << ptr2.parent_pointer() << '\n'
+              << "parent of " << ptr3 << " is " << ptr3.parent_pointer() << std::endl;
+}