[Feature request]: support for both us-imperial and uk-imperial when using .to("best", "unit") method.

[gorbypark]

The title says it all, really. I'm not even sure if .to("best", "imperial") is using US or UK imperial at the moment, but I have the need to display and convert between both.

Thanks for the great library!

[jonahsnider]

I believe "imperial" corresponds to US customary units. Which is confusing but my reasoning was that more people are familiar with the term "imperial" than "US customary" 🤷‍♂️.

Adding in support for UK imperial units should be fairly easy to do. What specific units did you have in mind as being different from the current US customary ones?