Also add check that current version appears in CHANGELOG in `publish` recipe, so hopefully I remember to update the CHANGELOG for the current release when bumping versions, not afterward :P
`env_var(key)` looks up the value of the environment variable with name `key`, aborting execution if it is not found.
`env_var_or_default(key, default)` looks up the value of the environment variable with name `key`, returning `default` if it is not found.
