Add support for format parameter in the command line

In order to call the rake task and get JSON output will be like so:

```
rake stats\[test/dummy,json\]
```

Author: etagwerker

lib/rails_stats/tasks.rb

@@ -1,13 +1,14 @@
 desc "Report code statistics (KLOCs, etc) from the current (or given) application"
-task :stats, [:path] do |t, args|
+task :stats, [:path, :format] do |t, args|
   Rake::Task["stats"].clear # clear out normal one if there
   require 'rails_stats/all'
 
   path = args[:path]
   path = Rails.root.to_s if defined?(Rails)
+  fmt = args[:format] || ""
   raise "no path given for stats" unless path
 
   root_directory = File.absolute_path(path)
   puts "\nDirectory: #{root_directory}\n\n" if args[:path]
-  RailsStats::CodeStatistics.new(root_directory).to_s
+  RailsStats::CodeStatistics.new(root_directory, format: fmt).to_s
 end