Macro managed_reexports

macro_rules! managed_reexports {
    ($crate_name:literal, $Manager:ty, $Wrapper:ty, $Error:ty, $ConfigError:ty) => { ... };
}

This macro creates all the type aliases usually reexported by deadpool-* crates. Crates that implement a deadpool manager should be considered stand alone crates and users of it should not need to use deadpool directly.