Add regular logging

[highvolt-dev]

Add diagnostic logging with loglevel support. Separate from #11

[AndrewPardoe]

I've started on this at https://github.com/AndrewPardoe/tmo-monitor/tree/logging. It moves errors to logging.error and adds an option to record connection characteristics, e.g.:

4G=B66 5G=n41 eNBID=12345 average ping=38

I don't have my modem for a couple days so I can't test this out.

[highvolt-dev]

Changes from @AndrewPardoe are merged in - open to any feedback from anyone while the next major release is in development