Prevent picturefill from running over the same image multiple times when loading async via polling
Merge remote-tracking branch 'scottjehl/refactor'
Changing picture to not re-evalute on elements that have already been evaluated, unless the force flag is set to true
Small tweaks, and namespacing `data-evaluated` to `data-picture-evaluated`
Merge pull request #139 from jansepar/master

Ensure that we don't repeatedly when loading async and polling the document for new picture elements