Use snake case in json reply

[noandrea]

currently the json keys are in pascal case, make them in snake case:

HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Headers: *
Access-Control-Allow-Methods: *
Access-Control-Allow-Origin: *
Content-Length: 409
Content-Type: application/json
Date: Tue, 09 Apr 2019 08:52:26 GMT
Vary: Accept-Encoding
Connection: close

{
  "ID": "ypxhlx",
  "URL": "xxxxx",
  "Counter": 0,
  "BountAt": "2019-03-29T11:15:02.500478396Z",
  "MaxRequests": 1,
  "ExhaustedURL": "",
  "TTL": 0,
  "ExpireOn": "0001-01-01T00:00:00Z",
  "ExpiredURL": ""
}