Added support for partials object

[pkuras]

jQuery Mustache plugin was missing support for partial objects which are supported by Mustache. From Mustache docs:

In mustache.js an object of partials may be passed as the third argument to Mustache.render. The object should be keyed by the name of the partial, and its value should be the partial text.

Mustache.render(template, view, {
  user: userTemplate
});

The patch adds support for such object. This allows to choose partial templates dynamically. For example, if template has partial with name {{> content}}, it is now possible to render some differently named template in place of this partial.

Here's an usage example:

        <script type="text/html" id="div">
            <div>
            Div content:
            {{> content}}
            </div>
        </script>
        <script type="text/html" id="content1">
            Hello world!
        </script>
        <script type="text/html" id="content2">
            Bye world!
        </script>

    $('body').mustache('div', {}, {}, {content: 'content1'});
    $('body').mustache('div', {}, {}, {content: 'content2'});

And the result:

Div content: Hello world!
Div content: Bye world!