MS Edge h descriptor fix

This plugin/polyfill fixes the missing h descriptor parsing in MS Edge by removing the h from all candidates of source and img elements and storing the physical aspect ratio of the candidates into a data-aspectratio attribute.

Note: This polyfill is already included in the respimg polyfill plugin and must not be included along site with it. But it is a good script in case you either use picturefill or do not use a polyfill at all.