I can create App Packages from Visual Studio 2013 using the wizard.
The result file is MyProject_Win8_1.1.1.3_x86_x64_arm_bundle.appxupload, which is fine!
I can use the following command to build an .appxupload file for any platform.
msbuild mysolution.sln /property:Configuration="Release" /t:"myproject_Win8" /p:Platform="ARM" /m:4 /t:"Publish"
which leads to generation of MyProject_Win8_1.1.1.3_ARM.appxupload
How can I tell msbuild to build all 3 platforms I need and generate one .appxupload file, which will contain them all?