Queue implementation is missing methods from the stock Queue class

[noteflakes]

Ruby docs:

First of all: close, closed?:

After the call to close completes, the following are true:

• closed? will return true
• close will be ignored.
• calling enq/push/<< will raise a ClosedQueueError
• when empty? is false, calling deq/pop/shift will return an object from the queue as usual.
• when empty? is true, deq(false) will not suspend the thread and will return nil. deq(true) will raise a ThreadError.

ClosedQueueError is inherited from StopIteration, so that you can break loop block.

Also: any ongoing blocking call to shift/pop should return nil once the queue is closed.

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Then we also have:

• deq - alias for shift
• enq - alias for push
• length - alias for size
• num_waiting - returns number of fibers currently waiting on queue
• deq/pop should also accept an optional nonblock=false parameter.