Parse module lib directories along with manifests

The `puppet yardoc` face now parses any files matching `lib/**/*.rb` when
operating on modules.
Separate Puppet namespaces from Ruby namespaces

The default YARD template lumps anything that inherits from `NamespaceObject`
into the "Classes" list in HTML output. This patch alters the list generation
logic so that Namespaces parsed from manifests are listed in a separate
"Puppet Manifests" list.
Add custom YARD handler for parser functions

This handler triggers on all occurrences of `newfunction` and parses the
parameters passed to that method in order to generate documentation. The
implementation is a good experiment in extracting documentation without
evaluating Ruby code. However, the generality of this approach may ultimately
be doomed by the use of metaprogramming in custom Types and Providers.