(PDOC-5) Add spec testing for face component

Add spec tests for Puppet face component, mainly around error checking.
Due to the use of `puppet module list`, the behavior of the `modules`
and `server` actions are not very feasible to test via spec testing.

Additionally, make a few minor changes to the gem file, and make a
small change in `check_required_features` to reflect the fact that
this module will no longer support anything earlier than Ruby 1.9.
(PDOC-5) Add spec testing for pops component

Prior to this commit there was no testing around the pops component.
Since most of the API in the pops component is private, there aren't
very many things to test, so add just a few test cases.

Additionally rename a previous spec file and make some changes to
the Gemfile.
(PDOC-5) Test defined types and 4x functions

Begin to test the YARD handlers written for the puppet language.
Add basic tests for the defined type and puppet 4 function
handlers. In addition, make changes to the spec helper to make it
easier to work with YARD Registries for testing purposes.
(PDOC-5) Test host classes and 4x functions

Add tests for the remaining two Puppet-specific handlers that were
not tested in the previous commit. Specifically, add tests for the
3.x function handler and the host class handler.