Support hiding annotation keywords when reporting errors

[Julian]

Sometimes a schema contains annotation-only keywords (particularly e.g. description or $comment) which effectively serve no purpose when reporting validation errors and essentially make the output longer / harder to read through.

While it would be nice if we had some even more fancy way of indicating what parts of the schema are relevant (e.g. via syntax highlighting and/or direct "arrow" pointing), a nice "cheaper" option would be to be able to render schemas without their annotation keywords (configurably).