Responsive images (handle multiple image sizes & resolutions)

Here are some ideas to improve how we handle images, that I had while thinking about #478:

Handling multiple image resolutions

The web has a standard that we could draw on to handle multiple image resolutions: the srcset and sizes attributes. Might this be useful to, for example, output a smaller PDF for screen than for print?

~Upgrade from isomorphic-fetch and alias fetch~

(separated out to #486)

~Also it might be good to take the opportunity to upgrade to cross-fetch which seems to be better maintained than isomorphic-fetch. We could alias fetch to cross-fetch at the same time:~

• ~Change import references from 'isomorphic-fetch' to 'fetch'~
• ~Install cross-fetch and alias it the same way we aliased yoga-layout-prebuilt in this commit~

[DuncanMacWeb]

@diegomura thanks! I’ve replied over at #486… so let’s change this issue to cover the multiple image resolutions / responsive images only.

[diegomura]

I just did the cross-fetch changes in a separate PR. Hope you don’t mind.

That change is great, specially because cross-fetch solves some issues un React Native that isomorphic-fetch, for future RN integration.

I kind of needed this change before moving forward with #485, so I can now have better (and fastest) tests using jest-fetch-mock