(CFACT-36) Add missing gem methods for Facter compatibility.

Adding missing cfacter gem methods for compatibility with the existing
Facter API and how it is used in Puppet.

Adding search, search_path, and search_external_path methods.  Currently
the search/search_path methods do not have any effect on fact resolution
as Ruby facts aren't yet supported. However, cfacter will store and
return the given paths.

Adding a [] method that returns a Fact object with name and value attributes.

Adding a reset method that clears the facts and also the search paths.