support native install/update/run in scripts

[maxandersen]

only missing thing for native is to enable autodownload/update of native binaries.

Idea is we will make OS specific bundles with:

jbang.sh|.ps1
jbang.jar
jbang-os-arch.bin|exe

and when native enabled jbang script will check if native binary available; if not download the bundle and run.
if no match or no internet fallback to run the .jar

this should also work for updates.