Display errors and warnings in a more human-readable format

[willosborne]

Feature Request

Description of Problem:

Currently validation report is output as a JSON object. We have a --format flag that lets you optionally set JUnit for XML output, but no option for easy human-readable data in a colour-coded table.

I think there's also room for a summary of the errors, so that you can see at a glance how many errors and validations there were.

Potential Solutions:

Add a new output mode that uses a library to display validation in a table, rather than as JSON. This may not even require a library - see the console.table() method: https://developer.mozilla.org/en-US/docs/Web/API/console/table_static

Coloured labels for errors would also help improve the glance value - one library I found was colors: https://www.npmjs.com/package/colors