Add back yardstick for documentation coverage

.yardstick.yml

@@ -0,0 +1,2 @@
+---
+threshold: 100

Gemfile

@@ -5,9 +5,11 @@ source 'https://rubygems.org'
 gem 'rake'
 
 group :test do
+  gem 'backports'
   gem 'coveralls', :require => false
   gem 'rspec',     '~> 2.14'
   gem 'simplecov', :require => false
+  gem 'yardstick'
 end
 
 platforms :jruby, :ruby_18 do

Rakefile

@@ -7,5 +7,16 @@ require 'rspec/core/rake_task'
 RSpec::Core::RakeTask.new(:spec)
 
 task :test    => :spec
-
 task :default => :spec
+
+require 'yardstick/rake/measurement'
+Yardstick::Rake::Measurement.new do |measurement|
+  measurement.output = 'measurement/report.txt'
+end
+
+require 'yardstick/rake/verify'
+Yardstick::Rake::Verify.new do |verify|
+  verify.threshold = 100
+end
+
+task :ci => [:spec, :verify_measurements]