Fix type name parsing in sphinx extension.

[YooSunYoung]

Fix #129

[jl-wynen]

What does the rendered docs look like with this?

[YooSunYoung]

With python 3.9

"""
    Parameters
    ----------
    event_weights_converter:
        A function to convert probabilities to event weights.
        The function should accept the probabilities as the first argument,
        and return the converted event weights.
"""
renders like:

And with python 3.10

But I couldn't find the way to make default not to include object address,
I ended up annotating them manually:

"""
    Parameters
    ----------
    event_weights_converter: :class:`~EventWeightsConverter`, \
        default: :func:`~event_weights_from_probability`
        A function to convert probabilities to event weights.
        The function should accept the probabilities as the first argument,
        and return the converted event weights.
"""

which renders like:

[YooSunYoung]

I think it makes sense to manually annotate them in this kind of special cases...