* Detect EOF signaling remote server closed connection
Raise ConnectionClosedByRemote and handle on `send`
* Fix linting
* Use existing NotConnected exception
* Add `Reader.is_connection_dropped` method
* Check connection before sending h11 events as well
* Add test covering connection lost before reading response content
* Check for connection closed on acquiring it from the pool
* Clean up ConnectionPool logic around reaquiry of connections
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