Use code coverage host

[jared321]

Based on my previous experiences, it would be good to add an extra step to our code coverage action that sends the final reports to CodeCov. This will provide a public interface for developers and others to assess the coverage of the test suite. In addition, it automatically adds coverage information to PRs.

[jared321]

@mpratola If you would like to add in this functionality, can you please hook this repo up with CodeCov and, if necessary, register a token with this repository so that our code coverage action can push results to the CodeCov server?

Once that's in place, I can update the action.