Add build script.

.gitattributes

@@ -2,3 +2,4 @@
 *.h	text
 CMakeLists.txt	text
 *.sh	eol=lf
+*.bat	eol=crlf

build.bat

+:: batch script for Windows build
+
+@echo off
+
+if "%cd%\" == "%~dp0" (
+  echo Please call the script from your build folder, for instance:
+  echo.
+  echo cd ..
+  echo mkdir build
+  echo ..\niflib\build.bat
+  echo.
+  pause
+  exit /b 1
+)
+
+cmake -G "NMake Makefiles" -DCMAKE_BUILD_TYPE=Release %~dp0
+nmake
+nmake package
+nmake package_source