[COOK-2254] (formerly CHEF-154) - replace runit_service definition with a service resource

This branch:

1. Implements runit_service as a service resource (subclassing Chef::Resource::Service).
2. Is incompatible with previous versions of the cookbook where the service resource was created and could be notified.
3. Includes a heaping pile of tests for great good, examples, and reference.
4. Includes COOK-2164, RHEL support.

It will be merged to master soon.