Add real wind speed calculations

[rafadodo]

The currently returned wind speed is merely the speed at which the anemometer rotates. But there is of course a difference between the former and the latter, dependant on the geometry of the anemometer. A better aproximation should be implemented.

[Bgeninatti]

I think a good approach could be, not to discard the current anemometer, but make a project structure that allows to add different kind of devices (even different kind of anemometers. Ultrasonic anemometer may be?!).
In this case we could add a better anemometer aproximation without discarding the actual easy and unexact aproach. But may be we first should make a better project modularization and documentation to make this in a ordered way