RFC: API design of package "modules"

pkg::fun() will call function fun from the namespace of package pkg
*without loading it onto the search path*

It is important to use conventional terminology here. The package (and
its dependencies) gets loaded but not *attached*. The `library` and
`require` functions load and attach a package in a single step. You
can also manually attach and detach environments to/from the search
path using the `attach` and `detach` functions.