win32 integration

These commits integrate the building of the audioencoder addons into win32. I've added the following:
* project/cmake/addons/CMakeLists.txt: cmake based buildsystem for binary addons. This might also work on other platforms and would be nice if most platforms could use this.
* project/cmake/addons/depends/win32/CMakeLists.txt: cmake base buildsystem for dependencies of binary addons. This is mostly based on @notspiff's work. Thanks for that.
* tools/buildsteps/win32/make-addons.bat and tools/buildsteps/win32/make-addon-depends.bat to prepare the environment, getting the binary addon dependencies and building the binary addons on win32.
* adjustments to the win32 installer to let the user choose which audioencoder addons to install.