compute: support BackendServices

[stephenplusplus]

For #1073

This implements Backend Services, known here as "services".

To Dos

• Tests
  • System
  • Unit
    • compute/index
    • compute/service

var service = compute.service('service-name');

service.getHealth({
  name: 'instance-group-name',
  zone: 'us-central1-a'
}, function(err, status) {
  status = [
    {
      ipAddress: '...',
      instance: '...',
      healthState: '...',
      port: '...'
    }
  ]
});

[stephenplusplus]

@callmehiphop I'm going to start on the unit tests, but let me know if you catch anything weird with the code.

[stephenplusplus]

don't merge lifted!

[callmehiphop]

Is there a docs preview for this?

[stephenplusplus]

Docs preview up: http://stephenplusplus.github.io/gcloud-node/#/docs/master/compute/service

RE: the missing callback param docs, that was an intentional decision back when we introduced the famous "get or create" overhaul. While having multiple methods to get at the same data can be convenient, the consequence was having to write the exact same documentation in multiple places. That has some hazardous side effects if the code is updated with a docs change local to the source method, the branched methods that reference it would go out of date. The chosen path was simply to have a link back to the source method from the branched methods and let the example do a quick and dirty job of showing what will happen in your callback. If you have any ideas how we can improve on this, open an issue so we can #️⃣ it out!

[callmehiphop]

Thanks for the preview! I think we need to add BackendServices to the site navigation via toc.json!

[callmehiphop]

This might not be the place for it, but are there are any JSDoc tags (aside from link) that would allow us to inherit the documentation from one method to another?

[stephenplusplus]

Not that I know of. Possibly the callback can be a "type" that we can then reference? I'm not sure if that's real / a hack usage.