Add log option to all outputs

[zuckschwerdt]

Logging used to be simple messages on stderr. Limitations:

• Always visible on the console (KV output), not available at other outputs (JSON, Syslog, HTTP)
• Not really inline with events (events: stdout, log: stderr)
• No severity visible (by color or common markers)

Logging now changed to be messages along the same path as events:

• Selectable for any output
• Inline with events
• Severity by color (or level markers)

Usage changes:

• If you don't select any outputs then logging will go to KV output (equivalent to -F kv, i.e. -F kv,v=8)
• If you select the KV output then logging will be shown, suppress with -F kv,v=0)
• If you don't select the KV output then no logging will be shown, add it with -F log)
• If you want logging back to stderr and suppressed in KV use -F log -F kv,v=0

Implementation

Now that refactoring from fprintf()s in decoders to decoder_log*() calls is done this will finally allow all logging to selectively (verbosity levels) go to outputs (KV, JSON, CSV, MQTT, HTTP, …).

One would raise the verbosity globally (-v) or per decoder (-R 99,v) and configure outputs to display those messages (e.g. -F json,v).

Tasks

• Outputs need to parse the level option
• Global prints ("noise level") need to be converted to log
• KV ouput should prettify the logs
• Looks like there is an overflow somewhere? (6e1f120)

[zuckschwerdt]

I'm pondering what label coloring would appeal to most? (dim or intense bg? regular or bold fg?)

The "intense-bold" variant is what we would use by default right now, the "dim" variants would be slightly more compatible with Windows 8.1 (only Windows 10+ offers bright bg).

The labels would show the logging "source" as seen here:

[zuckschwerdt]

Personally, I prefer the crisper looking non-bold text (also it's less of a distraction).
And the dim backgrounds might be a problem as many custom color schemes "wash out" those colors.
For me it then would be the first example above.

[zuckschwerdt]

Ok, let's use variant 1 for now (intense background, crisp non-bold text).

I'll merge this now. There is still need to fine-tune some log levels and messages, feel free to leave some feedback!