docs: def get_singlesig_privkey(privkey_info, blockchain='bitcoin', **blockchain_opts):
      """
      Given a private key bundle, get the (single) private key
      """
      if blockchain == 'bitcoin':
          return btc_get_singlesig_privkey(privkey_info, **blockchain_opts)
      else:
          raise ValueError('Unknown blockchain "{}"'.format(blockchain))