* Make blocking APIs optionally async
`DeviceInfo::open`, `Device::from_fd`, `Device::set_configuration`,
`Device::reset`, `Interface::set_alt_setting`, `Interface::clear_halt`
all perform IO but are currently blocking because the underlying OS APIs
are blocking.
`list_devices`,`list_buses`, `Device::claim_interface`
`Device::detach_and_claim_interface` theoretically don't perform IO, but
are also included here because they need to be async on WebUSB.
The `MaybeFuture` trait allows deferring these actions to the thread pool
from the `blocking` crate when used asynchronously with `.await` /
`IntoFuture`, or directly runs the blocking syscall synchronously with a
`.wait()` method.
14a8f171e5