A number of changes to accommodate streamlined, bundler-based gem dependencies:

- jekyll now included in Gemfile from forked puppetlabs/jekyll version
  We're using a specific branch rolled back to Jekyll 0.11.2 that includes a small patch
  to include _index.html (to accommodate YARD) and symlinked directories (to accommodate our
  MCollective setup)

- system(jekyll) calls changed to `bundle exec jekyll`
  Some day, if we ever get to a point where stock Jekyll can accommodate our needs,
  we'll be able to point the Gemfile to mojombo/jekyll and carry on. This frees us from
  going into the Rakefile and repointing the location of the jekyll executable

- yard docs generation included (using "developer" in rake tasks, e.g.
  rake:references:puppetdoc:developer)