Validations

[jpstroop]

Most classes have a note #validate.

It's an open question as to whether calling validate should raise errors or just accumulate a list of strings that indicate the problem (the latter approach makes it more like an ActiveRecord validation).

[minusdavid]

Personally, I'm trying to use https://github.com/IIIF/presentation-validator for validating manifests created with O'Sullivan and running into all sorts of issues...