Add screenshot generator for themes (and screenshots themselves)

lib/screenshot_generator.rb

@@ -0,0 +1,20 @@
+require 'lib/screenshot'
+
+class ScreenshotGenerator < ::Middleman::Extension
+  include Capybara::DSL
+
+  def initialize(app, options_hash={}, &block)
+    super
+    app.before_build do |builder|
+      Screenshot.prepare
+      data = YAML.load_file('data/themes.yml')
+      data.each do |theme|
+        Screenshot.new(theme[:name]).generate_theme_image
+      end
+      puts "Hello World"
+      # builder.run './my_deploy_script.sh'
+    end
+  end
+end
+
+::Middleman::Extensions.register(:screenshot_generator, ScreenshotGenerator)