Started updating the documentation
Minor refactoring/moving things around in the Breadcrumbs class
Breadcrumbs::setDivider() now accepts `null`

If configured to `null` (or an empty string), the divider will not be
rendered in the final HTML, which is how the new Twitter Bootstrap 3
works.
Added a test for divider-less output
Updated docblock for Breadcrumbs::setDivider()
Updated the documentation