Add .gitignore

Makes sense. Nevertheless, I don't think this is good idea, since this seems to be quite counterintuitive and I don't think it is really memory efficient. [HTML5ROCKS](http://www.html5rocks.com/en/tutorials/speed/v8/) recommends to "use contiguous keys starting at 0 for Arrays". Since you seem to care about efficiency, you might consider this worth merging. Probably this is a little bit of micro-optimization, but I don't think it's good practice to leave the first item empty.