Add support for checking Hiera YAML files

This includes a new `hiera` Rake task that assumes a `hieradata` directory
and a `hiera.yaml` file in the root of the repo.

Rather than tackle thornier problems around validating Hiera config, such as -
  - using Hiera itself to validate (Hiera.new, Hiera::Config.load etc.)
  - whether we're on version >3 or 2.7 of Puppet
  - various Hiera failure modes (hiera_include, hiera_hash, etc.),

I've opted for a simple YAML parse test - for now! :)
version: revert to 1.0.0
Make the hiera syntax check and specs 1.8-friendly
Namespace hiera tasks under syntax
Merge pull request #2 from andrewh/hiera-yaml

Add support for checking Hiera YAML files