add capacity to auto space items

Hi, here is another pull request ^^

Your view is great and helped me a lot. But I missed a feature for my project: it is to auto space items along the orientation if the total size is less than the associated layout size.

So my commit does this. It computes the space to put between each items and just use it instead of the startPadding, and the endPadding is discarded.

It could be completed to handle the paddings specified for each items, so that we do not auto space if the space used is less than the greatest padding of one of the item. It would prevent a wrong compression as the space get thinner if we had items.

But as it is, it helps with static layout with multiple views :)