Log to syslog

[hugoh]

Unifies logging to use logging and adds option to log to syslog.

Note that it works on Linux, and I cannot figure out why it doesn't on macOS (/var/run/syslog should be the socket to write to…).

Implements #54 on Linux, maybe on macOS too.

[highvolt-dev]

Thanks! Looks like I noticed two things:

1. The log format changed so the log level is no longer in square brackets. This affects parsing within delta logging as it is not updated to remove the brackets in its pattern declaration.
2. This PR introduces f strings which bumps up the python version requirement to be v3.6
3. I can't test against OS X either, but seems like we should give a runtime error and exit code 2 if syslog logging is enabled on a Windows platform unless we have it attempt to register and use the windows application event log with a distinct event source.

[hugoh]

I addressed all comments. Not sure how I ended up with a different log format to start with…

[highvolt-dev]

Thanks for the quick turnaround. Looks like the syslog_socket variable is referenced outdented from the block it is defined in the loop now.

Looks like we would want to adjust that reference, but beyond that, ready to merge your PR since we are in the middle of beta testing v2.0 and don't need this to be perfect

[hugoh]

Should be fixed. Thanks.

[highvolt-dev]

Maybe I'm tired, but looks like this would be missing whitespace before 'via'? Sorry for all the revisions!

[hugoh]

Oopsie. Fixed.

[highvolt-dev]

Thanks. The README is not up to date but I'll merge now! I can check out windows logging if I get the chance and document the system logging at that point perhaps? Thanks for your ongoing contributions!