Polygon Websockets & Aggregate Fix

In this release, we replace the old NATS connection for Polygon streaming with their new websocket endpoint. This change should be largely invisible to users, but we expect that the websocket connection will be more stable and reliable than the NATS connection was. If you wish to change the endpoint that the Polygon websocket attempts to connect to, you may specify it in the environment variable POLYGON_WS_URL.

Breaking changes:
This release also changes the names of Polygon aggregate fields on the v2 endpoint from their short version to their long versions. This is done for the sake of consistency with the rest of the SDK. Please note that if you were using v2 Polygon aggregates before this release, you will need to update your code to account for the long names.