Cherry picked commit @6250f7f from main picturefill repository: Older webkit compatibility fix to ensure that if there's a picImg already, that it's not the noscript fallback img. Credit to @simonwade for the fix.
Changed alias list for testing purpose
New organization of ngresponsiveimages.ini file.
Controlled html output of span elements by image alias instead of screens(MediaQueryExpression), adaptation to the new organization settings
Changed readme file - first draft
Removing responsive_image_alias dependency on definition in image.ini
Remove commented code
Merge branch 'master' into github_master