Initial, (non-working) support for GCE v1 API.
Add disk to server instance; remove image_name.
Prefer "instance" when talking about server + disk.
Delete disks by default on instance destruction; add option to toggle this.
More test coverage for v1 api support.
Rubocop style fix.
Add v1 API documentation (persistent disks), change reference to non-v1 image.
Merge branch 'feature-gce-v1-api'; closes #6.