Use phive (https://phar.io/) for installing apps

Hi there,

I just came across PHIVE (The PHAR Installation and Verification Environment) and it reminded me that the current phpbrew app command and that it could use some more love.
So I was wondering maybe phpbrew should use PHIVE instead of trying to build a custom app store.

Would you be interested in a PR that replaces the current app store with PHIVE?