Add tags to health checks

[orenht]

I would like to tag my health checks in order to divide them by subject, both for viewing and making a custom http report that reports only certain tags.

I assume this would involve changing the classes related to the health checks, and also all of the reporters... Maybe the default should remain as it is now, and an API will expose an option to report the tags too.

What do you say?

[orenht]

Hey, I created a pull request to solve this issue. Tell me what you think 😄

Pull request #70