While generally speaking the calling thread would have picked up the task first anyways, I don't think it makes much sense usually to block the calling thread until another thread wakes and does the work.
* Switch from the deprecated `multitask` crate to `async-executor`
* async-executor appears to be essentially multitask 0.3
* use block_on in futures_lite instead of pollster because futures_lite is already in the dependency list of async-executor
