* Allow users to create custom collections from other repositories.

Not sure if that should be part of crux.nu's portdb. I can see that
users create meta repositories, but I'm not sure if we should host
them. Or is this mean to be a private custom collection, or just a
special ports configuration file for a yet-to-be written ports(8)
driver that can merge repositories?

This idea was sort of inspired with the pull action I implemented in my
command line interface[1][2] to my current implementation of the
portdb[3].

Yes, this could theoretically be a future ports driver (and is planned).
The advantage here is that users could have a single ports repo on their
local system containing only the ports they use.