Register new shortlink

        Arguments:
            callback_uri:
                URI called by mCASH when user scans shortlink
            description:
                Shortlink description displayed in confirmation dialogs
            serial_number:
                Serial number on printed QR codes. This field is only used when
                registering printed stickers issued by mCASH

def create_shortlink(self, callback_uri=None,
                         description=None, serial_number=None):
        """Register new shortlink

        Arguments:
            callback_uri:
                URI called by mCASH when user scans shortlink
            description:
                Shortlink description displayed in confirmation dialogs
            serial_number:
                Serial number on printed QR codes. This field is only used when
                registering printed stickers issued by mCASH
        """
        arguments = {'callback_uri': callback_uri,
                     'description': description,
                     'serial_number': serial_number}
        return self.do_req('POST', self.merchant_api_base_url + '/shortlink/',
                           arguments).json()