Add feature: Read load balancer status.

The following two lines read the status of a load balancer.

    balancerManager = BalancerManager('http://your.domain/balancer-manager')
    status = balancerManager.getStatus()

The status is a hierarchical object. `status.clusters` provides a list
of clusters. Each cluster has a name (`cluster.name`) and a list of
members (`cluster.members`). Each member has several fields:

* workerUrl
* route
* routeRedirect
* loadFactor
* lbSet
* ignoreErrors
* drainingMode
* enabled
* hotStandby
* elected
* busy
* load
* transferred
* read