Wind speed averaging times as configuration option

[wcarthur]

Per request from Julie Plantaz, we should make the wind speed averaging time of the output a configurable option.

[wcarthur]

Add named wind speed averaging time to configuration options; Include a lookup table to determine the conversion factor, and the description to be used for the long name in the output file. May need to also modify some additional attributes for the wind speed variable in the output file. Suggested common definitions::

• 0.2 second gust;
• 3-second gust;
• 1-minute mean;
• 3-minute mean;
• 10-minute mean;

The reference period is a 1-minute mean wind speed - i.e. this is what the BL model generates with no modification. This also needs to be included in the output hazard file, and recorded on plots.

[wcarthur]

https://github.com/wcarthur/notebooks/blob/master/Wind%20speed%20averaging%20conversions.ipynb provides guidance on calculating wind speed averaging conversion factors, per WMO TD 1555