This reverts commit e64883eecb
and 40dd2d6923
Seems like core.run() returns once its done even if there
are still tasks in the Runtime underneath. A way to solve that
would be to call the shutdown_on_idle method.
We need ownership of the threadpool in order to invoke
`shutdown_on_idle` method but core.runtime only returns a
referrence so we need to create our own threadpool.
This requires a RUSTFLAG to be set before hand for rayon to build.
This brakes a lot of tools like rls and clippy by default and
require special configs for itnegration.
Additionally, rayon_futures is still 0.1 and not much work seem
to have gone into it. Ideally it should be replased with the tokio
runtime/threadpool.
