### Added

- `WithDispatch::inner` and `WithDispatch::inner_mut` methods to allow
  borrowing the wrapped type (#589)
- `WithDispatch::with_dispatch` method, to propagate the subscriber to
  another type (#589)
- `inner_pin_ref` and `inner_pin_mut` methods to `Instrumented` and
  `WithDispatch` to project to the inner future when pinned (#590)

Signed-off-by: Eliza Weisman <eliza@buoyant.io>