Implement RingQueue::resize()

[AvvALlV]

Implements #770

[gavv]

Hi, thanks for the patch and sorry for delay.

Here is a follow-up commit: d90cf31

I've changed behavior a bit: resize() now changes capacity(), not size(). Adding empty elements to the end of the queue seems to have little sense, and what we really need is just adding or removing extra memory. I also expanded the test a bit to cover this.