Make it possible to show rain volume

[cwitting]

This simply makes it possible to switch between showing Posibility of Precipitation (PoP) and rain volume in mm on the graph

[lmarzen]

I like this addition.
I have a few suggestions.
Some people may wish to change the unit. Particularly, I would advocate for an option to have the choice between mm, inches, and cm.
Second thing to note is that OpenWeatherMap has separate fields for rainfall and snowfall. I think we should add these fields so they are representative of the precipitation regardless of the season someone may be experiencing,

Let me know what you think?

[cwitting]

Yes, I agree. I have added another commit which makes it possible to specify the unit, as well as combining snow and rain precipitation.

[lmarzen]

Looks good, I'll test it out this weekend and merge it.

[lmarzen]

I have been busy with school work. I will try to get this merged over the thanksgiving holiday.

[lmarzen]

Overall this is a great contribution. Thank you.
I added automatic precision adjustments for the y-axis ticks to reduce the likelihood that the rainfall will run off the screen.