rework Windows build instructions

sys/windows/fetch.cmd

@@ -0,0 +1,30 @@
+@echo off
+if not exist lib\* mkdir lib
+
+if [%1] == [lua] (
+   set LUA_VERSION=5.4.6
+   set LUASRC=../lib/lua
+   set CURLLUASRC=http://www.lua.org/ftp/lua-%LUA_VERSION%.tar.gz
+   set CURLLUADST=lua-%LUA_VERSION.tar.gz
+   if NOT exist lib/lua.h (
+       cd lib
+       curl -L %CURLLUASRC% -o %CURLLUADST%
+       tar -xvf %CURLLUADST%
+       cd ..
+   )
+   echo Lua placed in lib/lua-%LUA_VERSION%.tar.gz
+)
+
+if [%1] == [pdcursesmod] (
+    set PDCVERSION=4.4.0
+    set CURLPDCSRC=https://github.com/Bill-Gray/PDCursesMod/archive/refs/tags/v%PDCVERSION%.zip
+    set CURLPDCDST=pdcursesmod.zip
+    if NOT exist lib/pdcursesmod/curses.h (
+        cd lib
+        curl -L %CURLPDCSRC% -o %CURLPDCDST%
+        tar -xvf %CURLPDCDST%
+        mkdir pdcursesmod
+        tar -C pdcursesmod --strip-components=1 -xvf %CURLPDCDST%
+        cd ..
+    )
+)