Docs: Update default stylesheets

Docs: Update default stylesheets

* colors pass the WCAG 1.0 for sufficient color
  contrast between the foreground and background

* visited links are no longer colored differently
  in the TOC and the nav bars

* link underlining is off by default in the TOC pane
  and nav bars but is retained in the hover state

* more improvements for the IE stylesheet

Signed-off-by: Patrick McCarty <pnorcks@gmail.com>
Signed-off-by: Reinhold Kainhofer <reinhold@kainhofer.com>