Add autolist package for automatic list animations

[benweitzman]

Autolist is a new package I've created to make it super easy to get beautiful animated lists without having to manage insertions + deletions manually.

Every time the contents of a list change, the Autolist widget will automatically detect the changes from the old list to the new list and use those to create animations.

All users of this library have to do is provide a list and a way to build a widget for each item of the list.

Tests + examples are included to make sure that this package is functional and easy to get started with.

Check it out on pub.dev at https://pub.dev/packages/autolist
Or view the source at https://gitlab.com/benweitzman/autolist

Quick demo:

[Solido]

Not maintained anymore, thx for PR !