Creates a new piece of Content.
        :param content_data (dict): A dictionary representing the data for the new content. Must have keys:
                                    "type", "title", "space", "body".
        :param callback: OPTIONAL: The callback to execute on the resulting data, before the method returns.
                         Default: None (no callback, raw data returned).
        :return: The JSON data returned from the content endpoint,
                 or the results of the callback. Will raise requests.HTTPError on bad input, potentially.

        Example content_data:
            {
                "type": "page",
                "title": "Example Content title",
                "space": {
                    "key": "TST"
                },
                "body": {
                    "storage": {
                        "value": "<p>This is a new page</p>",
                        "representation": "storage"
                    }
                }
            }

def create_new_content(self, content_data, callback=None):
        """
        Creates a new piece of Content.
        :param content_data (dict): A dictionary representing the data for the new content. Must have keys:
                                    "type", "title", "space", "body".
        :param callback: OPTIONAL: The callback to execute on the resulting data, before the method returns.
                         Default: None (no callback, raw data returned).
        :return: The JSON data returned from the content endpoint,
                 or the results of the callback. Will raise requests.HTTPError on bad input, potentially.

        Example content_data:
            {
                "type": "page",
                "title": "Example Content title",
                "space": {
                    "key": "TST"
                },
                "body": {
                    "storage": {
                        "value": "<p>This is a new page</p>",
                        "representation": "storage"
                    }
                }
            }
        """
        assert isinstance(content_data, dict) and set(content_data.keys()) >= self.NEW_CONTENT_REQUIRED_KEYS
        return self._service_post_request("rest/api/content", data=json.dumps(content_data),
                                          headers={"Content-Type": "application/json"}, callback=callback)