dpctl should generate C headers for use of dpctl Python objects with Python C-API

[oleksandr-pavlyk]

Torch extensions are built in C++ with use of pybind11 (c.f. custom-c++-torch-extensions).

One may want to recognize and work with SyclQueue, SyclDevice, and SyclContext objects, which requires a header.

Cython allows for generation of such headers: https://stackoverflow.com/questions/5710441/call-cython-function-from-c

[oleksandr-pavlyk]

Here is a discussion on SO: https://stackoverflow.com/questions/40572073/how-to-create-a-public-cython-function-that-can-receive-c-struct-instance-or-p

I adapted example written by @pelson based on suggestion in that SO post to Python3 and use in conda environment: https://github.com/oleksandr-pavlyk/calling_publicly_declared_cython_from_c

[oleksandr-pavlyk]

Another useful repo: https://github.com/ashwinvis/cython_capi

[diptorupd]

@oleksandr-pavlyk was this issue addressed by #218?

[diptorupd]

@oleksandr-pavlyk is going to add an example and close the issue.

[diptorupd]

@oleksandr-pavlyk ping!

[oleksandr-pavlyk]

Will work on this next week. Changes in #218 should have been sufficient, but having an example is both a proof of that and a seed to promote adoption

[diptorupd]

@oleksandr-pavlyk I believe the ticket can be closed?

[oleksandr-pavlyk]

What is still missing is a single "dpctl.h" to include to work with Python C-API of dpctl classes.

I think we should also have the same single header "syclinterface.h".

[oleksandr-pavlyk]

This has now been implemented in #685. Closing.