Add `Host` type

[usbalbin]

Add a Host type to interact with hosts. Some of the procedures available for hosts([see all_procedures.md](https://github.com/usbalbin/xo-api-client/blob/master/all_procedures.md for more)):

• [ ] host.emergencyShutdownHost host=<string> suspend all VMs and shutdown host
• [ ] host.restart id=<string> [force=<boolean>] restart the host
• [ ] host.setMaintenanceMode id=<string> maintenance=<boolean> manage the maintenance mode
• [ ] host.start id=<string> start the host
• [ ] host.stats host=<string> [granularity=<string>] returns statistic of the host`
• [ ] host.stop id=<string> stop the host