Add path to resolver errors

[tonyghita]

The request to add path to errors has been merged into the specification.

If an error can be associated to a particular field in the GraphQL result, it must contain an entry with the key path that details the path of the response field which experienced the error. This allows clients to identify whether a null result is intentional or caused by a runtime error.

This field should be a list of path segments starting at the root of the response and ending with the field associated with the error. Path segments that represent fields should be strings, and path segments that represent list indices should be 0-indexed integers. If the error happens in an aliased field, the path to the error should use the aliased name, since it represents a path in the response, not in the query.

The new specification is still unreleased, but it wouldn't hurt to start thinking about how we may implement this functionality.