update git submodule to reference latest commit at new repo
fix gendocset.py to work with Github repo format
add .gitignore for generated files and *~
add setup scripts and Make rules for setup/generation

Previously the build procedure was documented via comments in
gendocset.py.  This CL automates much of the prep & build.  The
automated version now also uses virtualenv and pip, in line with modern
Python dev practices.
Update packaged docset.tgz

Note that this was made with the package make rule.