Yield loaded translations to block in #load_translations

This makes introspecting the translations loaded by a file easier. Maintains backwards compatability as the block is optional.

lib/i18n/backend/base.rb

@@ -13,7 +13,10 @@ module Base
       # for details.
       def load_translations(*filenames)
         filenames = I18n.load_path if filenames.empty?
-        filenames.flatten.each { |filename| load_file(filename) }
+        filenames.flatten.each do |filename|
+          loaded_translations = load_file(filename)
+          yield filename, loaded_translations if block_given?
+        end
       end
 
       # This method receives a locale, a data hash and options for storing translations.
@@ -226,6 +229,8 @@ def load_file(filename)
             raise InvalidLocaleData.new(filename, 'expects it to return a hash, but does not')
           end
           data.each { |locale, d| store_translations(locale, d || {}, skip_symbolize_keys: keys_symbolized) }
+
+          data
         end
 
         # Loads a plain Ruby translations file. eval'ing the file must yield