Added windows directory for exe-based builds

Along with a configure script to generate a WiX installation
specification, and a template for WiX. Also deleted the XPM icon
(shouldn't be keeping derived bits around - should add a Makefile for
this and remove the PNGs too...)
Construct icons from SVG with Makefile

Removed all the PNG icons from the repository, and added a Makefile to
generate them from Inkscape. Need to make an .ico for Windows too...
Imagemagick?
Okay, actually removed the PNG icons this time...