Splitting the export list into various sections, to make nicer haddocks.

* Add `MonadSay` tracer, this allows to have outbound governor events
  in `IOSim` trace.
* Added `IOSim` trace to `prop_governor_gossip_1hr`: note that the
  simulations written by the governor never terminate,  so
  we must limit the trace output.

issues #3233, #3494, #3515, #3550

The outbound governor should first update its state from potentially
blocking decisions (monitoring connections, jobs, target and local roots
peers) and then look into non-blocking internal decisions.

This patch also fixes `prop_governor_gossip_1hr` which did not account
local root peers when checking the target number of root peers.  This
made the test depend on the order of events: with just two root peers
Public and Local, and `targetNumberOfRootPeers` set to 1; if `Public` one
was found first then the governor would still be looking to satisfy its
local root peer target, and it would find the `Local` peer; the test
would pass.  However, if the events where ordered differently, and
`Local` peer is found first, then the governor was not looking for any
more public root peers, and the `Public` peer was never discovered.

Closes #3460, fixes #3550

Check whether a peer is hasn't become cold when we try to update the
state once. In rare cases it could become cold just after we promoted it
to a hot peer, but before the completion continuation was scheduled.
This is because there could be a race between an asynchronous demotion
and the promotion.

Fixes #3550

If a mini-protocol errored, or handshake errored, we don't need to
`unregisterOutboundConnection`.  The connection handler thrown an
exception (either mux does it, or in the other case the handler itself).
When this happens, the finally handler will govern the evolution of
state of the connection: it will set it to `TerminatingSt`, close the
connection and wait for the `TIME_WAIT` timer, when eventually the
connection will be forgotten.

The `prop_governor_nofail` is a pure test which throws
`AssertionFailed`.  Run it in `IO` using `evaluate` to catch the errors
and print the trace log if it fails.  This relies on the property that
the trace will also encounter the same assertion failure.

As in the `outbound-governor: check the state when promoting a warm
peer` commit, but for the error handler.

Fixes #3494, fixes #3515.