DG: add library to generate RAF files
Add utility functions to generate RAF files (raw arbitrary waveform). Based on https://github.com/orealy/rigol-raf-generator/blob/master/raf_gen.py
Add utility functions to generate RAF files (raw arbitrary waveform). Based on https://github.com/orealy/rigol-raf-generator/blob/master/raf_gen.py