mina-circle token creation & error handling

[patricksimpson]

One thing that has bothered me for a while is the CircleCI auth token process. I'd like to simplify that.

• Create a setup script that asks for CircleCI token. It will create the mina-cirlce.yml file for you, if a token was not provided or this step was skipped, a placeholder file and token will be inserted.
• Error checking for missing or malformed CircleCI tokens.
• Friendly error message, to inform user that the token needs to be set if not done so by the setup.

Nice to have

• A script to edit or update the CircleCI token directly, instead of opening via an external editor.