Ibind

Fixes:

- `params_dict` recognises None when ensure_list_arg is applied to a None argument
- `make_order_request` accepts str and int for conid, always casting it to int. 'coid' is now an optional parameter
- `place_order` now accepts multiple order requests in order to facilitate sending bracket orders
- added rest_07_bracket_orders.py
- fixed `transaction_history` request method

- added positions2 endpoint
- added rest_06_options_chain.py
- fixed bug with reordering of 'bar' parameter in historical data endpoints
- added ensure_list_arg to 'live_marketdata_snapshot' fields argument
- changed snapshot_by_key dict values to string

* fixed wrong endpoint in live_marketdata_snapshot

First public beta release.

Initial alpha release