message: added optional params for pool
diff: from .libindy import do_call, create_cb
  +from typing import Optional
  from ctypes import *
  import logging
  async def create_pool_ledger_config(config_name: str,
  - config: str) -> None:
  + config: Optional[str]) -> None:
  logger = logging.getLogger(__name__)
  logger.debug("create_pool_ledger_config: >>> config_name: %s, config: %s",
  config_name,
  @@ -16,7 +17,7 @@ async def create_pool_ledger_config(config_name: str,
  create_pool_ledger_config.cb = create_cb(CFUNCTYPE(None, c_int32, c_int32))
  c_config_name = c_char_p(config_name.encode('utf-8'))
  - c_config = c_char_p(config.encode('utf-8'))
  + c_config = c_char_p(config.encode('utf-8')) if config is not None else None
  res = await do_call('indy_create_pool_ledger_config',
  create_pool_ledger_config.cb,
  @@ -28,7 +29,7 @@ async def create_pool_ledger_config(config_name: str,
  async def open_pool_ledger(config_name: str,
  - config: str) -> int:
  + config: Optional[str]) -> int:
  logger = logging.getLogger(__name__)
  logger.debug("open_pool_ledger: >>> config_name: %s, config: %s",
  config_name,
  @@ -39,7 +40,7 @@ async def open_pool_ledger(config_name: str,
  open_pool_ledger.cb = create_cb(CFUNCTYPE(None, c_int32, c_int32, c_int32))
  c_config_name = c_char_p(config_name.encode('utf-8'))
  - c_config = c_char_p(config.encode('utf-8'))
  + c_config = c_char_p(config.encode('utf-8')) if config is not None else None
  res = await do_call('indy_open_pool_ledger',
  open_pool_ledger.cb,
  