Posting keyboard events is deprecated in 10.9

As a temporary fix I am just raising an exception for now. For the
Future we have to find a different way. The only thing that comes to
mind right now is using CGEventCreateKeyboardEvent even trough that
can't be used to send a keyboard event to a specific element.
Merge pull request #10 from tbartelmess/keyboard-posting-deprecated

Posting keyboard events is deprecated in 10.9