* Migrate actix-threadpool to std::future
* Cosmetic refactor
- turn log::error! into log::warn! as it doesn't throw any error
- add Clone and Copy impls for Cancelled making it cheap to operate with
- apply rustfmt
* Bump up crate version to 0.2.0 and pre-fill its changelog
* Disable patching 'actix-threadpool' crate in global workspace as unnecessary
* Revert patching and fix 'actix-rt'