A trait representing requests to poll futures.
This trait is an argument to the
Spawn::execute which is used to run a
future to completion. An executor will receive requests to run a future and
an executor is responsible for ensuring that happens in a timely fashion.
Note that this trait is likely to be deprecated and/or renamed to avoid
clashing with the
future::Executor trait. If you've got a use case for
this or would like to comment on the name please let us know!