Remove more obsolete code
Move GetImports into Package

Again, this is part of the prelim work for being to support caching.
Move more functionality into Package

Also tidy things up a bit whilst we are at it ...
Move MakePkg into Package

This is the biggest bit of functionality that wasn't tied into the
Package type.  Though it still needs some work to make it caching
friendly ...
Make mkgomock a bit more user friendly
Don't process whole directories at once

We want to cache on a per file basis, so we want to stop processing a
directory as a unit.
More work on pulling out single file code

Again - we need to know what we are doing on a per file basis in order
to have appropriate hook points for caching.