Polling removed. Now callback based.

With Swig now supporting std::array I can finally dispose of any polling and python is now called with a callback interface whenever a sample has arrived. So even less computing time wasted.

This is all hidden away in the swig wrapper. The user just receives the samples via the callback at the given sampling rate and won't need to worry about anything else.

Sampling rate retrieval

Generally the driver is allowed to adjust the sampling rate if the requested sampling rate is not possible.

There is now a function where you can retrieve the actual sampling rate, in case the driver has altered it:

getSamplingRate()

As a rule of thumb sampling rates of 1kHz, 500Hz, 250Hz are always possible with the USB-DUX boards. Higher sampling rates are only possible if you use less channels.

Autodetect of DUX boards

The open() command now searches for DUX boards actively and not just opens the first comedi device.
The open(devno) command now creates an exception if the comedi device is not an USBDUX.

Bugfix release

There as been a spelling mistake in the hasSampleAvailable() function which has been corrected.
The examples folder now also contains a oscilloscope program which plots two channels at the same time.
A couple of simplifications of the functions starting the sampling.

Robust error handling even during mid DAQ USB disconnect

An exception is now also thrown when the USBDUX is unplugged while doing background async data acquisition so that it's possible to do a try/catch to detect a sudden disconnect and deal with it in software.

Now with Python exceptions

The comedi errors are now translated into proper Python exceptions. You can now use the "with" statement and also try/catch in python.

API change: adding open/close

In order to also have sync commands in the future I have created open/close and start/stop commands. open/close opens and closes the comedi device. start/stop starts/stop the async acquisition.