Store and display filename in results

[ryanstrickler]

I'd like to see filenames in my output when line or branch coverage fails and this change appears to work.

I'm using the minimum_coverage_by_file option in my test helper, but the current output doesn't seem helpful on it's own, especially in a CI context.

Maybe the intention is to force people to use the UI locally to find the files that need to be covered? But I think it would be helpful to my team if they could immediately see which file has an issue.

I will add tests to cover this, just wondering:

1. Is this something that has a chance of being merged into the main repo?
2. Am I totally on the wrong track with how to implement this? Is there a way to access the filename that I overlooked?

Example output:

Line coverage by file (0.00%) is below the expected minimum coverage (70.00%): /Users/ryan/Code/ryanstrickler/client/app/models/order_preview.rb
Branch coverage by file (0.00%) is below the expected minimum coverage (50.00%): /Users/ryan/Code/ryanstrickler/client/app/models/material_request_category.rb

If this is something that's been tried or shot down before, my apologies. I searched the repo and didn't see anything obviously related.

This is actually one of the first open-source PRs I've ever submitted, so be gentle. 😆