Pipelining the redis.get of the scalar data types and returning defaults.

Dear Ernesto,

For performance reasons I need to pipeline the gets of all my values which happen to all be scalar. Since the complex data types present more issues I decided to wait and see what you thought about the idea, and my implementation before continuing. As you can see, I also hacked in default handling. This is a convenience for me so that I don't have to write a bunch of defensive code for nil checking. My application doesn't expect floats and integers to be nil. This small mod means I don't have to check them. Overall, I think you've done a great job with this gem and I'm just tweaking it for my particular case. If you like my changes and would like to include them, I'd be happy to write the readme changes as well.