Fix archive title filtering to use specified post
Add breadcrumb to code reference landing page (otherwise there is no link to front page)
Various style improvements via samuelsidler:

* Fix padding on homepage
* Clean up handbook sidebar a bit, per mockup
* Open Sans the things, per mockup (and cleared with Siobhan)
* Handbook style changes including sidebar, topics box, and headings
Add handbook name header to the top of handbook pages
Allow customization of breadcrumb trail item container

* Add config option 'item_container'
* Use 'item_container' to wrap all breadcrumb items
* Allow suppressing 'separator' output by setting its value to false