Move Kernel#xy code into coordinate.rb.
Extract method save_error.

Consistent with ItemsParser#save_item and SettingsParser#save_setting.
Slightly improve error message.
Move String methods into req.

No longer needed within the application proper.
Add note about not refactoring some Rakefile code.
Remove superfluous comment.
Add method comment.
Clean up code a bit.
Move test helper code into test_helper.rb.