Use kebab-case value placeholders

[trueleo]

Description

Use kebab-case value placeholders in help/error messages.

example output:

error: The following required arguments were not provided:
  --username <username>
  --password <password>
  --s3-endpoint-url <url>
  --s3-access-key-id <access-key>
  --s3-secret-key <secret-key>
  --s3-region <region>
  --s3-bucket-name <bucket-name>

Usage: parseable --username <username> --password <password> --s3-endpoint-url <url> --s3-access-key-id <access-key> --s3-secret-key <secret-key> --s3-region <region> --s3-bucket-name <bucket-name>

For more information try '--help'