Minor API break: the longer RandomKey sits there, the longer it gnaws at my soul as an odd exception to the naming rules; best to fix now

Fix: Null RedisValue from boolean value

When implicit cast a boolen value into RedisValue the valueBlob was
setted to null.

Update KeysValues.md

Only prevent sync-continuations if explicitly enabled; otherwise it can cause near-deadlocks in the TPL-pool; avoid a dependency on the thread-pool in SocketManager

Fix: if calls Close or Dispose many times it'll throws a NullReferenceException

kill the unsent queue when connection fail; this is far more reasonable (expected), and ensures async works correctly

If the incoming socket isn't vanilla, we need to use async-read rather than socket-poll (the value of .Available is meaningless)