render_breadcrumbs now accepts a &block argument

This allows developers to customize how the breadcrumbs are rendered.

ex:

```haml
= render_breadcrumbs do |breadcrumbs|
  .container
    = breadcrumbs
```

This way, the container wrapper will only appear if there are breadcrumbs. Otherwise, if you did this:

```haml
.container
  = render_breadcrumbs
```

The `container` div would always be rendered.