Process Alazar buffers with C MEX file.

In my testing, I see a 2x speed increase. To use this, you need to move
into the @AlazarATS9870 folder and run "mex processBuffer.c". Then move
the resulting "mexw32" file into a folder on the MATLAB path. Should
probably properly make this a driver static method.

I've currently written things so that 'averager' and 'digitizer' now go
through a more similar code path. If this slows down the 'averager' mode
too much, it would be easy to go back to something more like the old
method.

--BRJ