Fixes API usage and possible division by 0 for wind speed

[PascalKern]

• There is no sub method on the time.ticks_xx() API'. So use of the time.ticks_diff(a, b) is the proper usage of the API.
• There is the possibility of having a division by 0 when the ticks are evaluated. I had this at least once.

It might fix some issues reported in: #99. At least will a division by 0 bringing the board into sort of a limbo state which might end freezing (RTC wakeup issue because of ZeroDivisionError)

Tested and running over a week without any issues on a weather board.

[ZodiusInfuser]

Hi @PascalKern, thank you for raising these issues. I was not aware of the ticks_diff function, so switching to that makes sense. It looks like there's other places throughout the code that need switching to that too.

[PascalKern]

Hi @ZodiusInfuser

Sorry my late reply. Some troublesome weeks behind and around me and not the time I want for coding etc.
Anyway. Finally some time! :)

First of all thanks for using my code updates and merging them. Secondly, you are very welcome I do like it when we can help out each other and improve our skills and knowledge. Open source is great! :D
To be honest I had a little help 😇 With PyCharm (a "propper" IDE ;)) such issues [ticks_xx has no sub] can be spotted much easier.

And thanks a lot for fixing all other instances of the ticks_xx - ticks_xx. I was only focused on the weather board and its issues.

Best, Pascal