Put experimental features behind Z-flags

[brson]

I mostly want to organize --help, and making these Z-flags removes at least 5 flags

[veddan]

Is there anything remaining on this issue or can it be closed?

[catamorphism]

I think this is done. I don't see anything obviously experimental under --help (except for an android-related flag, but that one has an argument, so maybe it's easiest to leave it as-is).