* Added page_props backend, generic parser-driven page properties which, when changed, invalidate the cache of backlinked pages on any links table. Could be used to add overlays to images depending on their deletion status, or to add icons to articles based on category membership.
* Refactored double-underscore handling in the parser.
* Moved CoreParserFunctions registration to CoreParserFunctions.
The parser now sets a "vary-revision" flag on the ParserOutput when using {{REVISIONID}}; Article then reparses the page after insertion if and only if required.
* JavaScript video player based loosely on Greg Maxwell's player
* Image page text snippet customisation
* Abstraction of transform parameters in the parser. Introduced Linker::makeImageLink2().
* Made canRender(), mustRender() depend on file, not just on handler. Moved width=0, height=0 checking to ImageHandler::canRender(), since audio streams have width=height=0 but should be rendered.
Also:
* Automatic upgrade for oldimage rows on image page view, allows media handler selection based on oi_*_mime
* oi_*_mime unconditionally referenced, REQUIRES SCHEMA UPGRADE
* Don't destroy file info for missing files on upgrade
* Simple, centralised extension message file handling
* Made MessageCache::loadAllMessages non-static, optimised for repeated-call case due to abuse in User.php
* Support for lightweight parser output hooks, with callback whitelist for security
* Moved Linker::formatSize() to Language, to join the new formatTimePeriod() and formatBitrate()
* Introduced MagicWordArray, regex capture trick requires that magic word IDs DO NOT CONTAIN HYPHENS.
* Clean up the mess in ParserOutput
* Reject (ignore) custom titles which don't normalise to the same as the current page -- THIS IS IMPORTANT OTHERWISE LINKING GOES TO POT (and not the good kind of pot)
[WARNING: Touches parser version. Old caches will be expired. You might wish to undo this and add some temporarily backwards-compatibility for a few days.]
* Add @addtogroup tags to various classes, to try and group conceptually-related classes together.
* Add brief descriptions to various Special pages, thanks to Phil Boswell.
* Moving some docs to be right above the classes they represent, so that they are picked up.
