Update CHANGELOG

Hack around a soundness issue

Prevent `CBox` from being opaquable if it isn't `Send`. This effectively
works around #18, albeit does not solve it. This will prevent `!Send`
futures from being turned into CGlue's opaque, `CBox: Send`.

Remove FastCWaker and VUB

Remove FastCWaker

Fix FastCWakerState drop code

Update CHANGELOG, fix old builds

Fix a borrowing safety bug in slices

Update changelog

Bump version, update CHANGELOG

Fix an oopsie