[META] allow multiple packages to be posted to a single package name

I've been thinking a lot about the issues caused by package name ownership.

1. Squatting
2. Bit rotting a package
3. Zombifying a package for exposure instead of passing it on to a new maintainer

This could be resolved if we allow multiple packages to be published under a single name.

Example:

`flutter_compass/hemanthrajv`
`flutter_compass/lukepighetti`

How would this work?

My proposal would be that anyone can create a package name, and they become the default, so in this case

`flutter_compass` is the same as `flutter_compass/hemanthrajv` because they created it.

But then I can come in later and publish my version as `flutter_compass/lukepighetti`

This avoids situations such as this https://github.com/hemanthrajv/flutter_compass/issues/43 where a package is no longer maintained, is missing features, and my only solution is to clutter up the pub namespace with a fork of an existing package.