docs: def download(self, sub_url):
          """download and unzip subtitle archive to a temp location"""
          response = requests.get(sub_url, headers=self.headers).text
          soup = BS(response, 'lxml')
          downlink = self.base_url+soup.select('.download a')[0]['href']
          data = requests.get(downlink, headers=self.headers)
          z = zipfile.ZipFile(cStringIO.StringIO(data.content))
          srt_files = [f.filename for f in z.filelist
                       if f.filename.rsplit('.')[-1].lower() in ['srt', 'ass']]
          z.extract(srt_files[0], '/tmp/')
          return srt_files[0]