Discuss and implement diagnostic levels

[eelstork]

Currently Debug-Chan does not offer diagnostic levels. For many projects, will not scale.

Ideas:

• Severity/LOD in general is not a great concept. A severity of 0, 1, 2, ... does not mean much. However, users may assign meaning to these (accept custom enums if easy enough)
• Debug-Chan is a logging tool. Its primary purpose is offering information beyond warnings and errors (happy to keep warnings and errors in the Unity console)
• Logging from public/protected/private... channeling based on this would be somewhat meaningful; don't think C# diagnostics include this but can get at it.

If there's a need to refine the debug chan APIs, how I see it -

• A log message expressing actual change (data write) is informative
• A log message clarifying control, but no mutation, is diagnostic
• Two-level messages including informative + diagnostic component may be good
• A QA API may be helpful to log key milestones which are also useful for validating features (as opposed to investigating issues)
• Ordinarily, we do not want objects to log when they can be described as "doing nothing" (quiescence rule) - that is, unless we think they should be doing something.

The core API should avoid overreach (log the way you want!); maybe attaching an int representing a channel / target will suffice; still, an optional API normalizing a good approach?