Saving wind data based on time interval (WIND_SAVE_INTERVAL) in seconds

If you want average wind data saved every 15 minutes,
- set WIND_SAVE_INTERVAL to (double) 15 * 60 sec = 900.0 
- change WIND_SAMPLES to (int) 900.0 / 30 = 30

I have an idea, which I will not implement myself:
The aneometer is sending data every 30 seconds and the pluviometer every 37 seconds. To reducing the total CPU load, the program could go to sleep (in function main()) after decoding a signal, until next expected transmission (minus 1-2 sec). Every 10th minute/transmission, it will NOT go to sleep for 40 sec, to get in sync if needed.

I think I am finished with this project for a while. My next approach would be to save data to a MySQL database on a different different server, to reduce write cycles to the SD-card.