I know that the documentation for `dispatch_queue_set_specific` says that keys are only compared as pointers, but using `self` as the key causes Xcode 8’s memory debugger to show `dispatch_set_specific` is strongly retaining self.  I know its not the case, but it makes it hard to track down other memory retention issues.

This commit changes the key from `self` to `_workQueue`.

Fixes #499. Make sure we don’t strongly retain to self while inside the timer.  Otherwise, its possible that the socket has been disconnected, the owner no longer has a reference to the object, but the object still lives in memory so long as the timer exists.

If you call `-open` then immediately `-close`, the `SRWebSocket` is marked as closed but:
1) The delegate never gets called that the socket did close
2) If `-openNetworkStreamWithCompletion:` ever invokes the completion block, the streams are left open
3) The `SRWebSocket` instance never calls `_cleanupSelfReference` and the object is strongly retained.

Fetch updates from vendor

Local updates (fine-tuning)

Fix memory leaks

0.5.1.2