Creates a new Client and begins asynchronously initializing it.
callback will be called when it is done; use new_async.end to get the result. Note that
on an error, the callback can be invoked with two first parameters as NULL.
NOTE: Client provides information about devices and a mechanism to control them. To access and modify network configuration data, use the RemoteSettings object.
| cancellable |
a Cancellable, or |
| callback |
callback to call when the client is created |
| user_data |
data for |