Separate entry point for Windows application.
Dropped object based approach for gui.

This is prerequisite for separated draw window and event window needed for
Windows version.
Separated drawing and event windows.

On Linux those are the same gtk.Window(). On Windows those will differ.
Added transparency support on Windows.

It's supported by Layered Windows [1]. There are two windows, event window
which is mostly transparent (alpha == 1) and drawing window with black
color key. Event window is needed because layered window with color key
does not handle events if cursor is in transparent region.

[1] http://msdn.microsoft.com/en-us/library/ms997507.aspx
Disable antialiasing on Windows.

It does not handle transparent Layered Windows properly.
Support switching transparency on Windows.

Antialiasing is enabled when transparency is disabled.