Rethink validation error representation

[travisbrown]

Currently this is a pretty slim wrapper for Everit's ValidationException, and there are probably some ways it could be improved. For a document with two schema violations, for example, there are three error values, since the top-level Everit exception ("2 schema violations found") is included.

[galatt]

Hello, I think it is possible to handle the violations based on keyword, also it would be great if the path could be returned in a format that Circe can handle. Currently it is in "#/key1/key2/3/key3" format. In our project we split the string, remove the root part, then we use circe-optics to get the violated field and the violation from schema jsons. Is there any work in progress for these upgrades?