Added minimal Importer class.
Importer sub-classes Sketchup::Importer
Added begin..rescue clause to load_file method.

SketchUp will BugSplat unless something is
returned in the load_file methods, and the
correct type must be returned (Integer)
Cleanup dead code, re-indent.
Merge pull request #4 from jimfoltz/dev

Now sub-classing Sketchup::Importer