Added DequeueSome and reduce array copying.

Modified DequeueAll to work more efficiently by ensuring that we don't reallocate the _items array and copy elements unless _size drops below the DEFAULT_CAPACITY (currently 16). Also added a DequeueSome for uses where we only want to grab N elements.
Merge pull request #14 from IDisposable/patch-1

Added DequeueSome and reduce array copying.