Improve: doesn't work with srcset

[bars3s]

Hi @OverZealous!

Found that cdnizer doesn't process srcset attributes. I think it will be very useful feature.

Thx!

[OverZealous]

Yeah, that definitely looks useful. That being said, that's a lot of work to integrate: the current design uses a RegExp-based replacement strategy that expects a (before)(url)(after) format, while srcsets are a comma-separated list of values, each of which has to be processed individually.

I'll see if I can find some time to add it in the near future.