NewJSONWriter creates a new instance of JSONWriter.

DefaultErrorCode - in case other codes are irrelevant.

EmptyRequestBody - when the request body is empty.

InvalidJSON - when the json data in request in invalid.

InvalidJSONField - when a json field in request in invalid.

RequestSizeExceeds - when request body's size is large.

UnKnownJSONField - when json request body contains unnecessary field for the request.

UnknownParseError - when the parse error is none of the above categories.

ValidationFailed - when the parse error is none of the above categories.

JSONWriter has functions for sending JSON response to client.