Alpaca-trade-api

In this release we add the ability to stop the websocket connection when using the data streams. Allowing the users to "pause/resume" their data stream.(d7e10ec51824947a010b7340b2162578844d4879)
We also add advanced usage example to help tackle the most common usage issues:
* pause/resume websocket connection (fc61ca97ac6d06d3aad6a79d39b1672c03634508)
* change the channels the websocket is subscribed to (85abc5874b0c3b4ce5d608b5f28cfba4e1ab4c72)
* websocket re-connection pattern, making sure we reconnect on ws diconnection (2902cb4a15816074da1374553faeb35b77cbc63a)
* different channels subscriptions for alpaca and polygon data streams.

In this release we enable raw data responses from REST and Stream APIs. (de0fc4f5dbc37ad1fada7624d2a68a9f27d63983)
It is achieved by passing `raw_data=True` to API instances and it returns the data without wrapping it with Entity objects. Default is using Entities, exactly as before.
Also:
* Support for polygon financials V2 (200f667d7779ddb0674aa1bb1190442ce1ef0f7c)
* Update the example code for websocket usage (a02e694faec15bb358aaa1c8daf3fde2be932e8d)
* Add oauth support for StreamConn (05f3a78ab12f9f06cdb5e9d7d1f1aa45c4b1b33b)
* Add CI pipelines for python 3.6-3.9 (be040630fb851edac27d09bbe0ea052c74ee0282)
* Make sure there are no issues with pandas 1.2.0+ and numpy 1.20.0+ which dropped support for python 3.6 (e2eb54d0efc3c4d522012e867ded4a181571a5d8)
Fixes
* handle better aggs empty response (e2c9b74edc1bdb817f46018d428d24ba66ed7f27)
* fixing dates for polygon queries (d84675eb490201dfe932f42283293f72398bfa81)
* fix should use asyncio.sleep inside async methods (c329fbae6f8fdb9696432a6e803e6f8160118e32)
* Calendar Entity dates (f848bdd46e1e31b8a37913302e4f9cd8e545f205)
* polygon grouped_daily() url (013cb801bf810f4b2d7452500bd28bfbee0cd9ea)
* update polygon trade mapping for Entity (8dbb10966353206842ba818fa8c574be97ba408c)

In this release we add support for the [alpaca-proxy-agent](https://github.com/shlomikushchi/alpaca-proxy-agent) which allows users to run multiple strategies in parallel.

also:
* Add a new simple stream example to demonstrate how to use the streaming service.
It's under `examples/websocket_example.py`
* Cleaner look for the documentation (README file)
* Explain exactly how to use `get_barset()`

Replace trailing stop orders are now supported by the API.

Adding it to the SDK as well

In this release we add support for the new added feature - trailing stop:
* submit_order now supports a new type `trailing_stop`.
* 2 new optional args to submit_order: `trail_price`, `trail_percent`.

Bugs
* Fix functions related to the Watchlist endpoint.

In this release we add small changes to help the user debug issues easily:
* Indicate that websocket is connected and to which endpoint
* add a debug flag to make websocket exceptions more verbose
* explain in the docs, how to define a logger to see these changes

Other changes
* We also removed the Alpha Vantage Integration. it will be moved to a stand alone package
* We now allow working with all versions of pandas (required for Pylivetrader)

Bugs
* fix bug with polygons' historic_aggs_v2 (https://github.com/alpacahq/alpaca-trade-api-python/issues/280)
* 'NoneType' object is not iterable (https://github.com/alpacahq/alpaca-trade-api-python/issues/270)