qdoc should generate output in an intermediate language using XML

When qdoc can generate documentation in an intermediate language such that each C++ class, C++ namespace, QML type, module page, text page, etc separate XML files, then qdoc can avoid generating all the documentation each time it runs because it can generate documentation for only those source files and include files that have a modified date/time later than the date/time of the last qdoc run, which can itself be stored in a small XML file in the designated output directory. When qdoc runs in this XML mode, it will not clear the output directory first but will simply replace the individual XML files for the C++, QML, and text entities that it modifies.

qdoc can produce a manifest of the XML files it updated, and this manifest will also be an XML file in the output directory. This manifest file and all the XML files it names as having been modified can be pushed to a documentation server, where each XML file will be converted to HTML and integrated into the QT documentation package there. This will allow rapid online inspection of documentation changes to ensure correctness.

Candidates for intermediate language include, but are not limited to, DITA and DocBook.