Build the docs.

def docs(session):
    """Build the docs."""

    session.install('sphinx', 'sphinx_rtd_theme')
    session.install('.')

    # Build the docs!
    session.run('rm', '-rf', 'docs/_build/')
    session.run('sphinx-build', '-W', '-b', 'html', '-d',
                'docs/_build/doctrees', 'docs/', 'docs/_build/html/')