win32 integration

These commits are necessary to get this addon working on win32.

* The first commit adds libFLAC_static as an optional name for the flac library as the archive we already have contains the library with that name and CMake doesn't find it because it looks for "flac.lib".
* The second commit adds the DLL to addon.xml
* The third commit adds the FLAC__NO_DLL preprocessor define to the win32 build because otherwise the symbols of the static flac library aren't properly recognized.