netcdf output should include important options used in the conversion as metadata

[garyjg]

Start with the min and max settings. The channel selection will be obvious from the file. Add a history attribute with the command line used. Eventually metadata could include the setting for whether timestamps were shifted or not, per #7. Probably it would be easier to add the metadata as attributes directly to the Dataset as it's being accumulated, as in #4 .

[garyjg]

• Related to which wind component should the hot film voltages be calibrated against? #2, the netcdf metadata should indicate the orientation of the probes, once we have an unambiguous way to identify the orientation.