Port status

[Bairdo]

goes on top of #39
and adds an interface for faucet to notify chewie of port status changes

[Bairdo]

Needs to set sm.portEnabled when port is up again. ATM i'm trying to get preemptive Identity Requests to be sent on port up.

[Bairdo]

Fixes #42 (timer scheduler).

Think preemptively sending identity requests on port up will need to be a separate PR. (issue #46)

[Bairdo]

closes #36

[byllyfish]

Just a heads up since I've been porting chewie to asyncio. Once you're confident in the heap-based scheduler, it would be worthwhile to refactor the scheduler into its own class (hiding the heap-based details):

An API that mirrored an event_loop call_later might look like this:

class TimerScheduler:
def call_later(self, timeout, func, *args): ...
def run(self): ...

https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.loop.call_later

This is not urgent, and I can submit a separate PR after this is pulled into master.

[Bairdo]

thanks for the suggestion.

this could be merged