Relax sized-ness constraint on `RefCnt`

[Marcus Weiner]

if i try to use the type ArcSwap<[T]> i'd expect it to be able to use a fat pointer the same way it works for Arc<[T]>

instead i get this compiler error:

error[E0277]: the size for values of type `[T]` cannot be known at compilation time
   --> src/proxy/origin.rs:47:24
    |
47  |     live_destinations: Arc<ArcSwap<[T]>>,
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    | 
   ::: /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/arc-swap-0.4.7/src/lib.rs:686:26
    |
686 | pub struct ArcSwapAny<T: RefCnt, S: LockStorage = Global> {
    |                          ------ required by this bound in `arc_swap::ArcSwapAny`
    |
    = help: the trait `std::marker::Sized` is not implemented for `[T]`
    = note: required because of the requirements on the impl of `arc_swap::RefCnt` for `std::sync::Arc<[T]>`

(note: T is sized)

is there a way to relax this constraint?

[Marcus Weiner]

oh, dupe of #27