64-bit build for MS Windows

[Antoine Martin]

There are a number of obstacles which prevent us from following the
instructions on ​dev/win32.

For some dependencies, it is just a question of doing more manual, as is the case for ​setuptools and ​python wmi.

Unfortunately, other dependencies are much much harder to deal with:

• ​pygtk (or even just plain GTK for that matter) do not provide 64-bit installers at present, and building from source is too tedious.
• ​gstreamer does not provide a 64-bit version, all the bindings are for 32-bit python only at present...