use Text::Markdown::Discount for both display and wala

- strip HTML::Defang
- get rid of old wala markup code
- use Discount for both markup modules (with NOHTML flag in wala)
tidy some basic config stuff
tweak p1k3.css font size
actual current p1k3 header (slightly tweaked)
default link titles in link_bar()
fiddle with lightweight markup functions

Just does an inline substitution for <textile> and <markdown> stuff.

Also adds a bit of commentary.
turn on extra footnote syntax in Discount

...mostly what this does is override the defaults of no headers / no
smartypants features.
local highlight.css