v4

Semver major bump, due to breaking, albeit minimal, changes:

1. The dist folder is no longer kept in the repository.
   It is instead available in the npm package and as an attachment in every release.
   Bower users may use CDNs such as jsdelivr (e.g. https://cdn.jsdelivr.net/npm/flatpickr/dist/flatpickr.js) or the npm package.

2. Locales and plugins in dist are now ES6 modules.
   This means you can use ES import statement, or keep using require with some changes.
   More info at https://chmln.github.io/flatpickr/localization/