Use inheritance_diagram.py provided by Sphinx (≥ 0.6).

Our inheritance_diagram.py doesn't work with the latest Sphinx
code, and upstream Sphinx has been shipping this extension
for many releases.
Merge pull request #111 from mitya57/master

Use inheritance_diagram.py provided by Sphinx (≥ 0.6)
Merge pull request #117 from arokem/travis-ci

NF: On the way to enabling travis ci.
Merge branch 'master' of https://github.com/nipy/nitime