Start work on issue #106: "distribution package" and "import package"

This is the start of a PR for issue #106 just to give people a chance to make early comments.

The glossary has been addressed so far, but I haven't reviewed all mentions of the word "distribution."
this is awkward.   it implies that "import package" is the official term, whereas it's really just a way for the PYPUG to distinguish it  from a  distribution package.