Perform deep merge of custom prefabs

Allows users to override parts of existing prefabs, i.e. individual
provider_specifics, without needing to duplicate facts.
Merge pull request #29 from domcleal/prefab-merge

Perform deep merge of custom prefabs
Fix yard doc error for Helpers

There was an error in helpers.rb due to the fact I copied a macro contents
but did not remove the usage of $0.

Also removed a couple of other little extraneous items, that I noticed.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'fix_yard_error'

* fix_yard_error:
  Fix yard doc error for Helpers