crazy optimisation to work around slow markdown

crazy optimisation to work around slow markdown

Markdown is slow. Especially if it has to process an enormous page. The
most common enormous page is currently the recentchanges page, which gets
processed a lot, and contains very little actual markdown. Most of it is a
big <div>, which markdown skips ... slowly.

This is a rather sick optimisation to work around markdown's speed issues.
Now inline inserts a small, dummy div, allows markdown to quickly render
the actual page content, then replaces the dummy with the actual inlined
pages later.

Results: Rendering just a recentchanges page, with diffs included, dropped
from 4.5 seconds to 2.7 seconds on my laptop. Building the entire wiki
dropped from 46.6 seconds to 39.5 seconds.

(It would be better if inline were a *post*-processor directive.)