Update domain function to return all scaled-positions rather than only [min, max]

[jo-chemla]

See #376 (comment)

[gka]

I think we should also adjust the test in test/scales.test.js for a multi-stop domain. And it make sense to update the documentation in docs/readme.md.

[jo-chemla]

Thanks for the feedback, just resolved both comments!

[gka]

perfect, thanks

[gka]

ah dang, just saw that the tests don't pass 😅. you didn't run them locally did you? going to submit another PR to address this.

[jo-chemla]

oh sorry about that, nope I did not run them I should have specified that. Will try to run them and fix

[gka]

I'll make sure tests are run on Github so this don't happen again :) see #381

[jo-chemla]

Alright, it now seems easier to maintain how you differentiate positions and domain, hope it won't break other parts of the implementation logic.
+ Nice catch for the expect(f(25).hex()).toBe('#ff0000'), sorry for this one
And also good to hear the tests will run on github at some point - that was my first reaction, go to github action to see the reason for the test not passing.