Add stream method to Query

Wraps events from the query object into a node v0.10.x Readable stream.
See demo https://gist.github.com/ZJONSSON/5314857

I also played with the idea of simply changing the Sequence object from an eventEmitter to a Readable stream (see https://github.com/ZJONSSON/node-mysql/commit/58ffaf3b81de54a5fabe79833de1f1a9b9fd7f31).   In that case the query object can be streamed directly without calling `.stream()`.  Original events dispatched as before.