Add BREAD_CRUMB_TRAIL.

Add BREAD_CRUMB_TRAIL.

This feature enables recursive printing of the bread crumbs for any
page, rather than just printing the parent group.

This is being used at nimbuskit.info. Example: http://v2.nimbuskit.info/NimbusKitCoreDataCodingConfigurationOptions.html.

![screen shot 2014-07-19 at 1 53 56 pm](https://cloud.githubusercontent.com/assets/45670/3634047/8056e3a8-0f11-11e4-9f13-c08269ed3db7.png)