Uncertainty treatments

[mankoff]

Supersedes #128

It would be nice to do proper and custom uncertainty propagation throughout the code.

Ideally, a final data product would match a CSV or NetCDF 1:1 with uncertainty / error at every data point at every time. Also related to proper flagging, where every variable at every time should be flagged with something that encodes 'best of', vs 'interpolated' vs 'filled' vs etc.

Uncertainty should consider flagged quality and propagation. For example, when interpolating station orientation, then all wind direction is impacted.