updated readme.
beautified Respec config.
Merge pull request #57 from ResponsiveImagesCG/fixed-respec-config

Fixed respec config
Merge pull request #58 from ResponsiveImagesCG/amended-abstract

Amended abstract
As this is a HTMLWG spec now, changing to ED
Merge branch 'fixed-sotd-section' of github.com:ResponsiveImagesCG/picture-element into fixed-sotd-section