Add `srcset` attribute on `img`.
Update transforms2d.json

See https://code.google.com/p/chromium/issues/detail?id=20574 etc.
Fixing typo in links section
Merge pull request #518 from ResponsiveImagesCG/srcset

Add `srcset` attribute on `img`.
Merge pull request #519 from iT-Rex/patch-1

Update transforms2d.json
Merge pull request #521 from frxnz/master

Fixing typo in webm links section
data update