Added config and logic (and demos) for aspectRatio (scale parameter).

Hi

I looked into full responsivity and it's logic and it's consequences and maybe one day I will complete it... But there are really a lot to consider...

But anyhow I implemented a small feature "aspectRatio" that for now covers our, Mobytechs and mine, needs and completes the expand-option so that the rescaling is kept to a constant factor (the aspectRatio). The idea and the purpose is (think small screens like phone-screens):
1) Set both dimension to 100%
2) with true aspect ratio there now should be some spaces in one of the dimensions since rescaling have been done according to the wanted aspect ratio and not eagerly in both dimensions.

Hope you can see the benefit with it. And feel free to adjust the examples…

So:
Implemented aspectRatio - a complement to the expand-option!