Your task is to implement a simple [RESTful API][restful-wikipedia] that receives [IOU][iou]s as POST requests, and can deliver specified summary information via GET requests.
| List of user information | GET | /users | `{"users":["Adam","Bob"]}` | `{"users":<List of all User objects>}` | `{"users":<List of User objects for <users> (sorted by name)}` |
| Create user | POST | /add | `{"user":<name of new user (unique)>}` | N/A | `<User object for new user>` |
| Create IOU | POST | /iou | `{"lender":<name of lender>,"borrower":<name of borrower>,"amount":5.25}` | N/A | `{"users":<updated User objects for <lender> and <borrower> (sorted by name)>}` |