Ensure uncaught yaml parsing errors are recoverable

[Mpdreamz]

We emit quite a few manual validations during parsing but this should ensure if something happens we didn't for see while parsing yaml in docset.yml or the front matters we:

1. Recover and continue compilation
2. Ensure we emit the exception through the regular error collector.
3. Ensure the error holds the originating file path.

The actual error will still be cryptic (yaml.net is just pretty cryptic) for uncaught exceptions. We'll continue to pre-empt these as we discover them to emit better error messages.