* timer: restructure feature flags
* update timer tests
* Add `async-traits` to CI
This also disables a buggy `threadpool` test. This test should be fixed in the future.
Refs #1225
A first pass at updating Tokio to use `std::future`.
Implementations of `Future` from the futures crate are updated to implement
`Future` from std. Implementations of `Stream` are moved to a feature flag.
This commits disables a number of crates that have not yet been updated.
Error::cause is deprecated in Rust 1.33, but this allows Error::cause
until the minimum supported version of tokio is Rust 1.30.
When the minimum support version of tokio reaches Rust 1.30,
replace Error::cause with Error::source.
Fixes: #817
Carl Lerche