Refactor the code in the strings face and extract much of the functionality
into a separate library in order to make the code more readable and
sustainable. Additionally, remove the `modules` action from the face
since it does not have a clear use case currently. However since the `server`
action depends on it, and it may be helpful to add other features in the future,
extract the functionality previously contained in `modules` into a helper
method.
Since we don't want the name of the tool to reflect the fact that
it is using yard internally (this is an implementation detail), rename
the face to `strings`. Now when one wishes to generate documentation,
`puppet strings` will be used rather than `puppet yardoc`.
Hailee Kenney