Enhancement: Broken reference detector should indicate file and line where offending resource was declared

[kpaulisse]

When the reference validation feature detects a broken reference, it currently prints messages such as the following:

Catalog has broken reference: cron::job[backup_to_s3] -> require[Aws::S3cfg[<fqdn>]] (OctocatalogDiff::Errors::ReferenceValidationError)

It would be much more helpful if this also printed the filename and line number where (in this example) cron::job { 'backup_to_s3': ...} was declared, to avoid searching through the codebase for it.

[kpaulisse]

Resolved by #103