(Maint) Remove unused example manifests

These manifests seem to have been created when some various issues were
fixed and functionality was added. However, they are not a comprehensive
(nor updated) example of how to use puppet. Keeping them here probably
ends up being a distraction for those who find them.
(Maint) Update commands to use new forms in hiera examples

The hiera examples were written assuming that puppet apply was just
puppet (the old form), and that hiera was not always available (and so
set the libdir).
(doc) Mark some of the Provider API public
Merge pull request #1937 from zaphod42/maint/master/cleanup-examples-dir

(Maint) Documentation fixes