Support traditional -y for automatically confirming a destructive action.

[fake-name]

The tugboat destroy command uses the non-standard -c argument for accepting deletion of a droplet silently.

-y, for "yes" is used for silently accepting changes in the great majority of other unix tools out there. Switching to the standard makes the adoption of this tool a lot easier for people who do a lot of command line stuff.

[petems]

Merged.

On a related note, please be considerate of the fact that this is free open-source software that people work on in their own time. Snark is not appreciated 👎