Use CSS rules to hang header permalinks

Header permalinks are now hung in the margin using `absolute` positioning.
A media query is used to disable this behavior on small screens, such as
phones, where margin space is limited.
Switch to font-stack-2

Consists of the following freely available fonts:

  - TeX Gyre Pagella, a Palatino derivative, for body text. Customized with
    support for small caps and old style figures.

  - Bitstream Vera Sans

  - Inconsolata, for setting source code and other monospaced items.