IMPROVEMENTS:
* Vendors package, adding provider specific functionality ([139](https://github.com/martinrusev/imbox/pull/139)) - Contributed by zevaverbach
* Type hints for every method and function ([136](https://github.com/martinrusev/imbox/pull/136)) - Contributed by zevaverbach
* Move all code out of __init__.py and into a separate module ([130](https://github.com/martinrusev/imbox/pull/130)) - Contributed by zevaverbach
* Enhance `messages' generator: ([129](https://github.com/martinrusev/imbox/pull/129)) - Contributed by zevaverbach