* Added plugin system, currently only supporting for PreProcessorDirectives.

* Added plugin system, currently only supporting for PreProcessorDirectives.
* Added a pagecount plugin, enabled by default.
* Support PreProcessorDirectives with no parameters, ie "[[pagecount ]]".
* Fixed/optimised backlinks code, to avoid rebuilding pages to update
  backlinks when the backlinks hadn't really changed.
* Moved inline page support, rss generation etc into the inline plugin,
  enabled by default.
* Added brokenlinks plugin, not enabled by default, but rather handy.
* Fix several broken links in the doc wiki.