Add ruby-hiera-eyaml package ready for backporting

These files are from the Ubuntu Utopic source package, obtained from:
http://archive.ubuntu.com/ubuntu/pool/universe/r/ruby-hiera-eyaml/ruby-hiera-eyaml_2.0.2-1.debian.tar.xz
Backport ruby-hiera-eyaml to Ubuntu Precise

Update `debian/changelog` and `debian/control` to backport the Utopic
package to Ubuntu.
Remove dependency on ruby-hiera

Hiera is provided by the Puppet Labs `hiera` APT package and no
`ruby-hiera` package exists for Precise, so remove the dependency.
Relax gem2deb dependency

The latest available `gem2deb` package available for Ubuntu Precise is
version `0.2.13`. The package still builds sucessfully with this
version, so relax the dependency.
Merge pull request #54 from alphagov/64650014-ruby-hiera-eyaml

[#64650014] Backport Ruby Hiera eYAML gem from Ubuntu Utopic to Precise