* establish new `node` folder for overseer, messages, and subsystems

* extract message types from overseer crate

* remove doc links

* Add block event forwarding into the Overseer

* Add a doc comment

* Fix a doc comment

* Adds start and stop work heartbeats.

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <[email protected]>

* Fix code after suggested changes

* Finalizing stops work on earlier lower blocks.

* Fix func parameter and flaky test

Co-authored-by: Bastian Köcher <[email protected]>

* Initial commit

* Licenses, spaces, docs

* Add a spawner

* Watch spawned subsystems with a FuturesUnordered

* Move the types around a bit

* Suggested fixes by Max

* Add a handler to talk to the Overseer

* FromOverseer and ToOverseer msgs and stopping

* Docs and return errors

* Dont broadcast, have add a from field to messages

* Allow communication between subsystems and outside world

* A message with a oneshot to send result example

* Remove leftover can_recv_msg

* Remove from field from messages

* Dont be generic over stuff

* Gather messages with StreamUnordered

* Fix comments and formatting

* More docs fixes and an example

* Apply suggestions from code review

Co-authored-by: Robert Habermeier <[email protected]>

* Fixes from review

Move function from impl block.
Do not panic but resolve with errors if spawner fails or subsystem
resolves.

* Dropping a handler results in a flaky test

Co-authored-by: Robert Habermeier <[email protected]>