[WIP] feat: support remote images

[lessp]

While experimenting with Revery I'm using a separate fork where I've, kind of naively, added support for remote-images. I'm opening so we can discuss and take the implementation further.

Questions:

• What to do about errors?

Would close #537

[bryphe]

Wow, this would be so nice to have 😍 Thanks @lessp for looking at this

[lessp]

I added Revery_Fetch which currently just wraps fetch-native-lwt in https://github.com/lessp/reason-fetch/.
I don't know if this is something we want to add now, it might be something for a later discussion 🤷‍♂

For Windows-support the main-blocker is:

ocsigen/lwt#745

which will solve:

lessp/fetch#18
lessp/fetch#14

And we'd also obviously want to handle the pin to anmonteiro's in order for it not to leak the resolutions.

https://github.com/revery-ui/revery/pull/642/files#diff-b9cfc7f2cdf78a7f4b91a753d10865a2R56-R58

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Also, I'm not sure how to make this work in JS, but feels like it shouldn't be too hard?

[lessp]

Closing in favour of #796