cl-cairo2 updates: win32 and mac extensions

Thanks to the contributions Kei Suzuki, cl-cairo2 underwent quite a few changes. Most importantly, as Kei contributed Win32 and OS X-specific code, I decided to separate all parts of the library that use a GUI. So now if you load cl-cairo2 (using ASDF), only GUI-independent parts of the library will be loaded. If you need the rest, you will have to load cl-cairo2-x11, cl-cairo2-mac or cl-cairo2-win using ASDF. All of these put their functions in the :cl-cairo2 package, without creating a new one, so the organization of namespaces is simplified. Also, cl-cairo2 and the GUI extensions are still packaged into a single tarball, which you can download or install directly using ASDF-Install. Here are some screenshots contributed by Kei Suzuki: You can find the code for these in tutorial/lissajous.lisp and tutorial/lissajous-win.lisp.