"package"-local modules

[PaulBone]

We need to find a way to explain this succinctly without saying Packages, or accept that's the term we'll use and go with it. But it's not a concrete thing.

Support modules that are local to a group of modules (export symbols those may import) but not to outside that group. Groups (aka packages) are defined by heirachy. Eg: Net.HTTP and Net.FTP may both import a local (maybe "private"?) module Net.Utils, but MyApp may not use Net.Utils directly.

Depends on #316 because it's going to interact with libraries and #260

[ACleverDisguise]

Cluster?

[PaulBone]

For the name of a group of modules. maybe? I think "library" is fine though.

Also i don't mind the fun nuclear physics related names but only if there's a certain amount of things we name in this way to make it worth while / make sense / maybe even grain raction and accelerate. Some kind of critical mass of nuclear physics puns.