Add units option to display Fahrenheit

[markfickett]

This is great! I couldn't get TCView to work on Windows, and this worked right away.

I unfortunately think in the bad units, so it would be very convenient to have C to F conversion as an option.

[rich123]

I just pushed to my fork the ability to cycle through temperature units (K, C, or F):
https://github.com/rich123/PyThermalCamera.