Features
* added Kubernetes API objects:
* `Role`
* `ClusterRole`
* `RoleBinding`
* `ClusterRoleBinding`
* `StatefulSet`
* `HTTPClient` learned to handle GKE OAuth authentication
* `HTTPClient` learned `version` to report Kubernetes version
* `Pod` learned to retrieve logs for containers
* `Query.filter` learned to scope based on fields
* Fixed handling of Kubernetes certificates for Python versions < 3.5
* Kubernetes 1.5 compatibility
* `APIObject` learned `metadata` and `labels` properties
* `KubeConfig` learned `namespace` and depedent objects use it more sanely