Update change notes for _find() and _update()

This adds the `versionchanged` notes for the changes to the behavior of
`_id` added in 605088a.

References #18
Add html command to Makefile

This new option is a shortcut for the `make html` command already found
in the documentation Makefile. It can be used to create the HTML version
of the docs without having to change to the docs directory first.
Move publish from setup.py to Makefile

Moving the `publish` command to the Makefile will keep setup.py a bit
cleaner. As an added bonus `make publish` is less typing than
`python setup.py publish`.