Async validation support

[olvnikon]

Description

Нет поддержки асинхронной валидации. Учитывая асинхронность effector, данная библиотека тоже должна уметь работать с асинхронными валидациями. Например, должна принимать effect как функцию валидации.

[aanation]

@olvnikon
Yes, this is in the plans and will probably be included in the new major release. Do you have a vision for the API?
Do you want to pass effects along with the usual synchronous validation rules or instead? Should it be possible to pass multiple effects? Is the order important?

In general I need ideas on APIs based on your cases