(maint) Make stdlib usable as a Ruby GEM

(maint) Make stdlib usable as a Ruby GEM

Without this patch it is inconvenient to use the functions included in
stdlib in a development setting.  The Puppet modulepath must be
explicitly set for the functions to be automatically loaded.

This patch addresses the problem by adding a gem specification and
dependency Gemfile.  This makes it possible to directly use stdlib and
all of the components it depends upon, like so:

    $ bundle install --path .bundle/gems/
    $ bundle exec puppet apply -e 'notice count([1, 2, 3])'

The first command will install all of the dependencies, including Puppet
and Facter, into the local project directory.  The second command will
make stdlib avaialable as a Gem, which will be picked up by Puppet since
(#7788) was merged into Puppet in the 3.0 release.