besseres build script

build.bat

@@ -1,12 +1,12 @@
 :ReleaseWin64
 SET RETURN=ReleaseWin64
 SET NEXT=ReleaseWin32
-"%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" "SMP.sln" /p:configuration=release /p:platform=x64
+"%InstallDir%\%MSBuildExe%" "SMP.sln" /p:configuration=release /p:platform=x64
 if errorlevel 1 GOTO Error
 :ReleaseWin32
 SET RETURN=ReleaseWin32
 SET NEXT=END
-"%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" "SMP.sln" /p:configuration=release /p:platform=win32
+"%InstallDir%\%MSBuildExe%" "SMP.sln" /p:configuration=release /p:platform=win32
 if errorlevel 1 GOTO Error
 GOTO End
 :Error