Support Actix 4.0.0

[suptejas]

This library does not support versions of actix-web greater than the latest version 3 release (3.3.3). It would be awesome if Actix version 4 support is added in!

[kmindi]

I also ran into a problem using it, couldn't compile anymore because of the dependency on actix-http = {version = "2.2.0", features=["actors"]} which then depends on a conflicting brotli version leading to a linker error (see actix/actix-web#2698)