Be explicit when requiring formatters.

I think I prefer this explicitness over the prior
automatic importing code. It feels safer (it won't
load files that are placed into the formatters
folder that shouldn't be there) and it avoids the
issue we had in #145 where formatters can load in
arbitrary order.

lib/twine.rb

@@ -28,6 +28,14 @@ module Twine
   require 'twine/output_processor'
   require 'twine/placeholders'
   require 'twine/formatters'
+  require 'twine/formatters/abstract'
+  require 'twine/formatters/android'
+  require 'twine/formatters/apple'
+  require 'twine/formatters/django'
+  require 'twine/formatters/flash'
+  require 'twine/formatters/gettext'
+  require 'twine/formatters/jquery'
+  require 'twine/formatters/tizen'
   require 'twine/runner'
   require 'twine/version'
 end

lib/twine/formatters.rb

@@ -18,8 +18,3 @@ module Twine
     end
   end
 end
-
-require File.join(File.dirname(__FILE__), 'formatters', 'abstract.rb')
-Dir[File.join(File.dirname(__FILE__), 'formatters', '*.rb')].each do |file|
-  require file
-end