4.0.0 released!

[benkeen]

I just released version 4.0.0 of this script which has a whole slew of new improvements, including the option for integrations with other scripts like Material UI, Fluent, react-select and others.

I kept the API pretty much identical to the previous versions, but do note the breaking changes listed here.
https://github.com/country-regions/react-country-region-selector/blob/master/CHANGELOG.md

Please report any issues you run into.