have wrapplets use the signature of the slave

def wraplet_signature(app, what, name, obj, options, signature, return_annotation):
    """have wrapplets use the signature of the slave"""
    try:
        wrapped = obj._raw_slave
    except AttributeError:
        return None
    else:
        slave_argspec = autodoc.getargspec(wrapped)
        slave_signature = autodoc.formatargspec(obj, *slave_argspec)
        return (slave_signature, return_annotation)