Add basic (working-ish) specs

The tests pass, but due to what appears to be a bug in rspec-puppet,
changing hiera_config does not appear to be effective, so to run the
tests, run `rspec` on each spec file directly:

    $ rspec spec/functions/hiera_genders_broken_spec.rb
    $ rspec spec/functions/hiera_genders_good_spec.rb
Add metadata & docs