Support enabling breadcrumbs

[jwodder]

Example breadcrumbs:

Template	Breadcrumbs
tags.html	Home » Tags
tag.html	Home » Tags » Tag Name
article.html	Home » Archive » Article Title

• For article breadcrumbs, if period archives are in use, use those instead of (or following?) "Archive".

• This will require making use of {CATEGORIES,AUTHORS,TAGS}_URL settings.

• Add "» Page N" to the end of breadcrumbs when not on page 1