Various fixes

* Do not hard code config directory.
* Support .yaml or .yml files.
* Spew a debug message when using default values.
* Fix modulepath lookup for Puppet >= 2.7
* Raise ParseError if the YAML files are not valid.
* Sort keys before returning from get_var('foo', 'foo:keys')
* Fix tests for puppet >= 2.6
* perltidy tests.