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/travis-gcc.sh

@@ -0,0 +1,8 @@
+set -x
+mkdir -p lib
+cd lib
+git clone --depth 1 https://github.com/wmcbrine/PDCurses.git pdcurses
+#git clone --depth 1 https://github.com/universal-ctags/ctags.git ctags
+curl -R -O http://www.lua.org/ftp/lua-5.4.3.tar.gz
+tar zxf lua-5.4.3.tar.gz
+cd ../