Print, but don't fail on deprecation notice

A simple change so that deprecation notices are printed, but don't cause test failures. A possible fix for issue #27.
I don't think we should filter based on the value of `fail_on_warnings`. As a user I would not expect the `warnings` array to be empty because I had set `fail_on_warnings` to true; rather I'd expect to get an array of warnings but that would not cause a failure.

I think we should separate the errors and warnings in `manifests.rb` and keep the failure logic in `lib/puppet-syntax/tasks/puppet-syntax.rb`.

Thanks for your work on this, I'm happy to help with the tests once we've finalised the implementation.