Doxygen (merge post 64-bit)

Since @pjrobertson mentioned doxygen comments somewhere (pull request #815), I decided to finally get serious about that. I pushed the current documentation to the gh-pages branch of the Quicksilver repo. So now it's available from http://quicksilver.github.com/Quicksilver/Reference/. I also added a few things:

* A doxygen config file (see Tools/Doxygen) used to create the documentation. To use it, you have to install [Doxygen for MacOS](http://www.stack.nl/~dimitri/doxygen/download.html#latestsrc) and [graphviz](http://www.graphviz.org/Download_macos.php) (to create nice releationship-graphs). You can than run Doxygen.app, load the config file and build the documentation yourself.
* To make it easier to create the documentation **and** add it to the XCode help, I added a target to the Quicksilver XCode project called "Build Documentation". Just run it, and when it's finished (it takes quite a while), the documentation is available (and searchable) inside the XCode help. Of course it also needs Doxygen to be installed.
* Added another target called "Upload Documentation". That one builds the documentation as well and then pushes an update to the gh-pages branch. Only works, when you're on the master branch. I'm not sure yet if this is really a good idea, but I like to automate it as much as possible.