Add support for isinstance() checks. #201

[GrahamDumpleton]

Going to close and reopen this to try and force ability to run tests via GitHub actions. Option not showing.

[GrahamDumpleton]

Didn't pay attention close enough when I merged. After the fact I simplified the C code to:

static PyObject *WraptFunctionWrapperBase_instancecheck(
        WraptFunctionWrapperObject *self, PyObject *instance)
{
    PyObject *object = NULL;
    PyObject *result = NULL;

    int check = 0;

    if (!self->object_proxy.wrapped) {
        PyErr_SetString(PyExc_ValueError, "wrapper has not been initialized");
        return NULL;
    }

    check = PyObject_IsInstance(instance, self->object_proxy.wrapped);

    if (check < 0) {
        return NULL;
    }

    result = check ? Py_True : Py_False;

    Py_INCREF(result);
    return result;
}