Update to using f-strings instead of sting.format()

[bsimmo]

Update to using f-strings instead of sting.format()

Is your Feature Request related to a problem? Please describe.
This is just a nice to have.
f-strings are the new Python3.6+ method and are apparently much faster* especially in later python3's and for me easier to read too.
try a search on are f-strings faster than .format

Describe the solution you'd like
Change all strings from .format to f-string

Describe alternatives you've considered
No alternative other than no rush as not vital, 1-wire is slow anyway, but every little helps.

Additional context
Something for a rainy day.
It's the way forward for Python3
It does mean a drop of Python3.5 support (support for 3.5 has been dropped by Python)

[timofurrer]

Something for a rainy day.

Absolutely! I kept Python 3.5 support because of Raspbian stretch which comes with Python 3.5
However, I'm down for dropping it.

Feel free to use your next rainy day and submit that PR 😄