Aloe should have code coverage

[jhomarolo]

Is your feature request related to a problem? Please describe.
Code coverage is a metric that can help you understand how much of your source is tested. It's a very useful metric that can help you assess the quality of your test suite.

Describe the solution you'd like
Aloe should have the code coverage feature.

Describe alternatives you've considered
Maybe an integration with Istanbul (https://github.com/istanbuljs/nyc) or similar should resolve the problem.

[dalssoft]

Does it need to be integrated to Herbs or Istanbul is decoupled enough?

I wonder if just running nyc herbs spec with a few tunings would get the results for the code coverage