Pull request: add log level "warn" for more complete audits

[Cameron Cundiff]

Hi folks,

Can someone please review my pull request: https://github.com/Casecommons/capybara-accessible/pull/1

Supports a configuration of Auditor to set log_level to :warn. This will log the audit failure messages without stopping the test. It may be a way to get a more comprehensive audit of workflows. There is a risk of introducing a lot of noise and duplicate warnings.