Consider adding breadcrumbs to the navigation

[DannyBen]

Perhaps it will be useful to have the navigation builder also add breadcrumbs on top of all the navigation pages?

This could either be done by the builder itself, or, if we opt to use a completely custom theme, it might be possible to implement it in the theme layout itself (see #3).

Potential Solutions:

1. jekyll-breadcrumbs
2. jekyll-breadcrumb-for-github-pages
3. StackOverflow answer