Paca

This is another pre-release for 0.47. In this release we:
* removed the polyfeed prefix
* better exception handling for stream2
* support the new data schema:
* trade in WS: rename “sym” to “T”, “t” to be nanoseconds (from milliseconds)
* quote in WS: no change
* bars in WS: rename “sym” to “T”
* trade in REST: timestamp resolution is now nanoseconds
* quote in REST: timestamp resolution is now nanoseconds
* bars in REST: no change

This is another pre-release for the upcoming Alpaca Data API upgrade. This release notably changes the default streaming connection from polygon to alpaca. The caller can still choose polygon with `data_stream='polygon'` in StreamConn initializer.

This is the first RC release to support new Alpaca Data API.

- get_last_trade()
- get_last_quote()
- StreamConn() can now connect to streams of trade, quotes and minute bars

The API specification changed after the release of v0.45 - timestamps are now provided in milliseconds rather than seconds. This update fixes the dataframe's index.

As it says in the title, support has been added for a couple new endpoints.

Polygon open/close: https://polygon.io/docs/#!/Stocks--Equities/get_v1_open_close_symbol_date
Documentation for Alpaca portfolio history is forthcoming, but is documented as such in the readme for the moment:

REST.get_portfolio_history(date_start=None, date_end=None, period=None, timeframe=None, extended_hours=None)
Calls GET /account/portfolio/history and returns a PortfolioHistory entity. PortfolioHistory.df can be used to get the results as a dataframe.

The Alpha Vantage package added in the last release was not declared in setup.py, leading to some installation issues. We've added it now, so it should be picked up when you try to run the SDK.