Doxygen documentation update:
* Changed alls @addtogroup to @ingroup. @addtogroup adds the comment to the group description, but doesn't add the file, class, function, ... to the group like @ingroup does. See for example http://svn.wikimedia.org/doc/group__SpecialPage.html where it's impossible to see related files, classes, ... that should belong to that group.
* Added @file to file description, it seems that it should be explicitely decalred for file descriptions, otherwise doxygen will think that the comment document the first class, variabled, function, ... that is in that file.
* Removed some empty comments
* Removed some ?>
Added following groups:
* ExternalStorage
* JobQueue
* MaintenanceLanguage
One more thing: there are still a lot of warnings when generating the doc.
* Reduced stack depth by using an internal stack in expand(), and by having some common code paths (e.g. non-subst double-brace during PST) return objects which can be expanded in that internal stack instead of the PHP stack. This is friendly to xdebug but slightly slower than the original version. Also it probably helps robustness when you don't add 7 stack levels per pair of double braces.
* Profiling indicates that expand and PPD are now good targets for porting to C. Abstracted and refactored the relevant code to allow for a drop-in replacement. A factor of 2 reduction in average-case replaceVariables() time may be possible.
* Verified with preprocessorFuzzTest.php against r29950, updated to allow better PST tests.
* Made parserTests.php respect $wgParserConf
* LST and ParserFunctions need a simultaneous update with the core due to changed interfaces. DOM objects are now wrapped rather than directly exposed.
