Return default parameters passed to Axes.annotate to create labels.

def initial_annotate_kwargs():
    """Return default parameters passed to Axes.annotate to create labels."""
    return dict(
        xycoords="data", textcoords="data",
        rotation=90, horizontalalignment="center", verticalalignment="center",
        arrowprops=dict(arrowstyle="-", relpos=(0.5, 0.0))
    )