Build documentation as HTML.

    The build HTML site is located in the ``doc/_build/html`` directory
    of the package.

def build(ctx):
    """Build documentation as HTML.

    The build HTML site is located in the ``doc/_build/html`` directory
    of the package.
    """
    return_code = run_sphinx(ctx.obj['root_dir'])
    if return_code > 0:
        sys.exit(return_code)