Fiddle around with post markup and styling.

  - Move post notes into the same element as the post body and metadata,
    because semantics blah blah blah.
  - Change post-related styles to work with the new markup. As a
    concequence, layout rules now concern themselves only with layout,
    just as nature intended.
Change post metadata classes to use BEM syntax.
Change page navigation classes to use BEM syntax.
Add Typekit stuff.