-moved copying of huge data (adwaita icons) to install_data stage
instead of build_exe stage to minimize copyings count.
-pygobject-win32 support dropped
-worked around autoinclusion of gdiplus
-disable bytecompilation of files included in
lib\python3.6\site-packages\meld\
since they can be used only by humans reading source,
not by freezed executable
-simplify zip building by providing empty install prefix by default

-appveyour build broken by now, but appveyour.yml has a new cmdline
for fast building zip and msi from single folder,
which eliminates one more copying of icons.