Added Dart impl. in C

[dhikshithrm]

Hello Wolt Team.

We have ported the C implementation over to dart through dart:ffi, because the pure dart implementation was very slow and it was causing UI freeze.

Our package published over on pub.dev, fixes that issue with the same api for the developers that previously used blurhash_dart and flutter_blurhash.

you may merge it you think it's a good addition to this repo.

[dhikshithrm]

Thanks for the info, that makes sense, removed the submodule section.

[jerry-git]

Thanks! 🍬