Delete old Snapshots first and Docker Support

Delete before creating new snaps (#84)

according to the docs https://cloud.google.com/compute/docs/disks/restore-and-delete-snapshots#deleting_snapshot this would be slightly more correct since instead of gcp handling the magic of references, we can allow the newly created snapshot to reference the right parent

Bug Fix: --filter clause disks list

Fixing --filter clause on disk name (#80)

Previously was only picking up disks with same name as instance

Use --filter to target instance

Use --filter to target instance (#79)

Fixing a bug that was re-introduced with 5.0.0

Add Project Id option

Added a project id option -j so that the script can be run to backup multiple projects without needing to change the gcloud config core.project each time.

Use coloured output for Errors & Debug

Uses tput to colour output

Minor Bug fixes

• Throw error if no devices are found
• createSnapshotName() positional typo
• Restrict custom prefix to 20 chars

Fully supporting Remote Instances and clean-up of Options

Script now fully supports Remote Instances with [-r <remote_instances>] option - no need to pass in Instance name and zone.

Removed [-t <label_name>] as this functionality can be achieved using [-f <gcloud_filter_expression>] (which was previously [-T <gcloud_filter_expression>].

Also added Dry run for debugging.

Large amount of code was changed.

Updated README to include auth instructions

Update README.md (#57)

* Update README.md

If your gcloud on the server isn't authenticated for your Google Cloud, you'll get an error that looks something like:
```
ERROR: (gcloud.compute.disks.list) Some requests did not succeed:
 - Insufficient Permission
```

* Update README.md

Flexible filter for choosing disk to snapshot

4.0.3

Merge branch 'pr/56'

Add support to use a specific service account

Add support to use a specific service account via command line (#54)

* Add support to use a specific service account via command line

* Updated Usage

* Fix typo