Wrap render function in SWIG threads macro, to disable Python GIL

[stephen322]

My attempt at issue #98 -- a new wrapper function to disable Python GIL during rendering.
It-Works-For-Me...

This is so unrelated Python threads can run while ws2812 does its thing. I'm not trying to imply rpi_ws281x is thread-safe.

Not sure why the SWIG-generated files have different formatting than what was there.
I used "swig -python -threads".

[stephen322]

Ah, files are re-formated by black.
Amended commit.

[Gadgetoid]

Thanks for putting in the effort to PR this. I don't use WS281x pixels as much as I did when I first adopted this library, so I'm pressed for time and incentive to give it a proper test.

Any drive-by volunteers who fire up this code and find the changes useful, your comments would be very helpful!

[stephen322]

This patch was designed to make its use optional, so in theory should be the same as before.
Although there is the new threading import dependency in python for the mutex, and I wouldn't know what other things swig might do behind-the-scenes with threading enabled...