Add an option that allows you to hide all files where code coverage is full in the code coverage output

[carlos-granados]

Inspired by this Pinkary post: https://pinkary.com/@huberfe/questions/9d38b8f9-dc41-46ff-9708-0a6cf90eaac7

If your project has very good code coverage where most files are covered (like the Pinkary project), you may want to remove from the code coverage output all files where coverage is already 100%, allowing you to concentrate on those files which have not reached this level without having to hunt them down amongst a long list of green files

This PR adds a new --hide-full-coverage option to the test command. When this option is passed, any file where code coverage is 100% will not be printed in the test output

Also currently the code coverage section did not have any kind of header which explained what was being displayed, I added this header and a little explainer if this option is selected

Once this PR is merged, this option can be added to Pest (and any other testing tool that might use this repository)