Support multiple webroots

[nikolay]

There are some use cases where multiple packages should be installed under different webroots. Any plans to do this using similar technique as the Composer installer?

[sbuzonas]

I had considered it but didn't quite have a need for it. I couldn't wrap my head around a clean way to do it in my initial implementation. Circling back now I should change the configuration extra to be an array of webroot packages where it takes hashes of package => directory