Hierarchical modules

[LightAndLight]

Currently only 'sibling' modules can be imported, i.e. import a. I might want to allow importing 'child' modules, i.e. import a.b.

I haven't yet decided if I want this feature.

If I do implement it, the 'missing import' error messages should be good. In import a.b, account for a missing a and also account for a missing b.

[LightAndLight]

There's potential for ambiguity here. Does a.b mean "the binding b in the a module" or "the submodule b of a"?