Enable typed and untyped tags (terms) with namespace and label support

[shah]

Add to frontmatter for indexing

folksonomy:
  - untyped-tag-1
  - [untyped-tag-2-value, Untyped Tag 2 Label (No Namespace)]
  - [untyped-tag-3-value, Untyped Tag 3 Label, ut3namespace]
  - term: untyped-tag-4-value
    label: Untyped Tag 4 Label
    namespace: ut4namespace
taxonomy:
  - typed-tag-1
  - [typed-tag-2-value, "Typed Tag 2 Label"]
  - [typed-tag-3-value, "Typed Tag 3 Label", t3namespace]
  - term: typed-tag-4-value
    label: typed Tag 4 Label
    namespace: t4namespace
relationships:
  - type: SYMBOL
  - type: ../page/page/
  - type: /page/page/
  - type: ./page/page/
behavior:
    lexer:       # any search-specific behaviors

• [X] folksonomies
• [X] taxonomies
• [ ] For relationships the type would be a taxonomy term and can point at one or more pages by SYMBOL (#51) or relative/absolute paths.