Windspeed conversion operators

### What problem does your feature request solve?

Sometimes windspeeds need to be converted from different factors. Currently we do not have this functionality as a stand alone operator.

### Describe the solution you'd like

A set of windspeed convertors to extend those currently in 'wind.py':
- horizontal windspeed (from u and v)
- total windspeed (u, v, and w)
- horizontal wind direction (from u and v)

### Describe alternatives you've considered