change references from winnt to windows

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.

sys/windows/vs/tilemap/aftertilemap.proj

@@ -0,0 +1,12 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="..\dirs.props"/>
+  <Import Project="$(vsDir)files.props"/>
+  <Target Name="Build"
+     Inputs="$(ToolsDir)tilemap.exe"
+	 Outputs="$(SrcDir)tile.c">
+	<Exec Command="&quot;$(ToolsDir)tilemap.exe&quot;" WorkingDirectory="$(SrcDir)"/>
+  </Target>
+  <Target Name="Clean">
+	<Delete Files="$(SrcDir)tile.c"/>
+  </Target>
+</Project>