Support of multiple 'engines'?

[mefistotelis]

Since KMD supports currently only SMBus 2.0, and the message length is restricted even more by length being included in the bytes limit, I had to implement SMBus using I2C commands.

Maybe smbus2 itself should include such implementation? There could be a selection option on whether messages should be constructed by kernel or by python. I'd call it 'engine' selection, or 'api' selection.. not sure what's the best name.

This would also allow support of other 'engines' in the future - for example, for USB-to-I2C bridges, which typically are visible as USB HID device, there is a library smbusb. That library can also be used on Windows. I might work on Python bindings for it in the future.

So available 'engines' may depend on OS - the list should be dynamic.