Generate and reply headers

def _send_headers(self, status_code=200, content_type='application/json', more_headers={}):
        """
        Generate and reply headers
        """
        self.send_response(status_code)
        self.send_header('content-type', content_type)
        self.send_header('Access-Control-Allow-Origin', '*')    # CORS
        for (hdr, val) in more_headers.items():
            self.send_header(hdr, val)

        self.end_headers()