Get names of fit parameters from a ``scipy.rv_*`` distribution.

def param_names(scipy_dist):
    """Get names of fit parameters from a ``scipy.rv_*`` distribution."""
    if not isinstance(scipy_dist, rv_continuous):
        raise TypeError
    names = ['loc', 'scale']
    if scipy_dist.shapes is not None:
        names += scipy_dist.shapes.split()
    return names