Add a getInstance() method to CodeIgniter Hook.

I'm not sure if there is another way to do this already. But this allows for the current instance of Clockwork\Clockwork to be accessible from elsewhere in the application. So from my base controller, for example I can write:

    $this->clockwork = Clockwork\Support\CodeIgniter\Hook_Clockwork::getInstance();
    $this->clockwork->info('Log Something');