Provider status (done, running, not run) is now attached to the
provider-specific data of the client. A reference count of auth
instances is kept in the auth_client struct to determine if a client is
done or not.
This also moves a lot of the logic for manipulating provider data into
into the provider.h header for inlining (no point in a function call for
these simple accessors).
Clients are stored in a dictionary referenced by id (to allow for
UINT32_MAX auth clients, which is plenty).
Each provider now has a data slot (this limits the number of providers
to 32 for now, but that's plenty for now) which they can use to attach
data to auth_clients. This consolidates data, aids in debugging, and
makes it easier to just pass around auth_client structures.
