Subclass-ability

[teodoryantcheff]

Playing around with your module I wanted to create a subclass of the SpiDev class, but found it impossible. After some poking around Python docs I added a Py_TPFLAGS_BASETYPE flag and all seems to be fine and my app works. Not sure is that's all that needs to be done ...
Since it's only a one line change, didn't want to create a full blown pull request so here's the diff :

diff --git a/spidev_module.c b/spidev_module.c
index f39a761..c9413aa 100644
--- a/spidev_module.c
+++ b/spidev_module.c
@@ -798,7 +798,7 @@ static PyTypeObject SpiDevObjectType = {
        0,                              /* tp_getattro */
        0,                              /* tp_setattro */
        0,                              /* tp_as_buffer */
-       Py_TPFLAGS_DEFAULT,             /* tp_flags */
+       Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,               /* tp_flags */
        SpiDevObjectType_doc,           /* tp_doc */
        0,                              /* tp_traverse */
        0,                              /* tp_clear */

Please let me know if you see merging this into master as a workable idea. Thanks !

Cheers,

Teo