The NetHackW.res file wasn't being forced to be rebuilt if
the tiles were changed as they were recently.
Fix the Makefile.msc dependency so that it is.
Also have 'nmake clean' clear the generated *.res files.
rename sys/winnt to sys/windows
move vs (visual studio) folder out of win/win32 and into sys/windows
rename include/ntconf.h to include/windconf.h
rename winnt.c to windsys.c
place visual studio projects into individual subfolders.
This will hopefully resolve GitHub issue #484 as well.
