write python parser for nidas dat files

[garyjg]

It may be helpful for this project to be able to read the hotfilm voltages directly from the nidas dat files rather than parsing the values from the data_dump text output. I've resisted this idea in the past, preferring not to have implementations of the nidas dat format in multiple languages, but really the disk format is not too complicated and it may not be hard to write a decoder in python, at least for the uncompressed format, as used by the hotfilm data files.

A python decoder may also make it easier to pull out specific diagnostic variables in the hotfilm data, such as the per-channel 1-second means.