added a railtie, shifted the mime types out

lib/publicious.rb

@@ -1,6 +1,7 @@
-Mime::Type.register "image/jpeg", :jpg
-Mime::Type.register "image/gif", :gif
-Mime::Type.register "image/png", :png
+if defined?(Rails)
+  require 'publicious/railtie'
+  require 'publicious/mime_types'
+end
 
 class Publicious
   FILE_METHODS = %w(GET HEAD).freeze

lib/publicious/mime_types.rb

@@ -0,0 +1,3 @@
+Mime::Type.register "image/jpeg", :jpg
+Mime::Type.register "image/gif", :gif
+Mime::Type.register "image/png", :png

lib/publicious/railtie.rb

@@ -0,0 +1,3 @@
+class PubliciousRailtie < Rails::Railtie
+  config.app.middelware.insert_before(Rack::Lock, Publicious) if config.respond_to?(:app)
+end