Integrate status information at arti-client
This commit combines status update information from tor-dirmgr and tor-chanmgr in the arti-client crate, so that the user can get to it; it represents a high-level view of the client's ability to reach the network and route traffic. I have omitted the tor-circmgr support for now; it's mostly not needed. At present it's not so useful, since there's no way for a client to get a TorClient that _isn't_ completely bootstrapped, and therefore there's no way to actually watch these events until they're no longer interesting. That should change with arti#293. This is part of #96.