counter can now be a jquery object

# What is this?

This PR enables the user to pass a jQuery object as a `counter:` in the options parameter.

# Why would you want to do that?

If you're dynamically creating multiple textareas on the page, then you can have all your counter elements have the same selector. You just pass in each specific element when you're initiating each textarea manually. For example:

```
$(document).ready(function(){
  $('textarea').each(function(){
   var counter = $(this).closest('.textarea-container').find('.counter');
    $(this).simplyCountable({counter: counter});
  });
});
```