java code not strictly required

[lumenkeyes]

Per Android Developers, if an apk is created with android:hasCode="false" in the manifest, android's apk tools will happily build it without adding any Java code. Perhaps the check in apk.zig could be turned off with an option? I could submit a PR with a quick change I made, you just have to use it like this:

const apk = android.APK.create(b, android_tools);
apk.hasCode = false;

Can rewrite if you'd like a nicer interface, but would be nice to have some way to turn off the check

[silbinarywolf]

Done.

Added follow-up issue to explore adding validation back in here:
#34