Use Queue API instead of inefficient operations

[okumin]

In Scala 2.10.x, Queue#:+ has a performance issue. https://github.com/scala/scala/commit/f0f0a5e7813501d985174d3c5573c34c8a7608c6

So this commit replaces that operations with Queue#enqueue. And use Queue#dequeue explicitly instead of Queue#head and Queue#tail. There is little dirrerence between these operations, but it will be obvious that Queue is used correctly.

[okumin]

When I tried to request too many commands, Queue#:+ in ResponseHandling spent much time.

[debasishg]

Thanks .. I will take a look and merge ASAP.

[okumin]

I found another bottleneck……, so I'm going to fix that.

[okumin]

It is difficult to fix, so created the issue. https://github.com/debasishg/scala-redis-nb/issues/104