Peers
-----

A peer is an entity which has exactly one address book that is meant
to be cached locally. Typically a peer is a phone connected via
Bluetooth and accessed via PBAP, but it could also be a web service
that supports CardDAV or a phone with SyncML support.

Address books
-------------

Address books which mirror data from a specific peer use the string
"peer-<uid>" as ID, where <uid> is the unique ID of that peer.

In addition, there is a system address book which is independent of
any particular phone. Its ID is the empty string.

APIs
----
Manager.Start/Stop - startup control
Manager.GetActiveAddressBooks/SetActiveAddressBooks - control unified address
book content
Manager.SetPeer/RemovePeer/SyncPeer/StopSync/GetAllPeers - configure and
control syncing