Containers allowing multiple selector matches

[treyhunner]

This change allows the form field selector to match multiple elements with a common parent selector that contains the target counter element.

For example this Javascript:

$('.my-field').simplyCountable(
    counter: '.my-counter',
    container: '.my-container',
    maxCount: 30
});

Would work as expected with this markup:

<div class="my-container">
First Name: (limit <span class="my-counter"></span> characters): 
<input name="first_name" class="my-field">
</div>
<div class="my-container">
Last Name: (limit <span class="my-counter"></span> characters): 
<input name="last_name" class="my-field">
</div>
<div class="my-container">
Email: (limit <span class="my-counter"></span> characters): 
<input name="email" class="my-field">
</div>

Diff with whitespace differences ignored.