Add support for wsrv.nl

[kevmodrome]

Is your feature request related to a problem? Please describe.
wsrv.nl is a free image resizing service that has been running since 2007.

Supports image manipulation via URLs: https://wsrv.nl/docs/quick-reference.html

Describe the solution you'd like
Added as a provider would be great.

Describe alternatives you've considered
Use another provider

Additional context
Nothing to add.

[ascorbic]

I'd be happy to accept a PR

[kevmodrome]

Didn't realize I was in the wrong repo. 😓 I'll try to open a PR in the unpic repo.

[kevmodrome]

Do I also need to do something in this repo to get the provider added?