Added additional severity levels and ability to customize levels.

[bokysan]

This commit:

• Aligns the severity levels in loggo with syslog severity
  levels. This makes it easier to export logging through loggo
  directly to syslog.
• Enables the user to customize / define custom severity levels.
  Some users like to define levels such as TRACE1, TRACE2 and
  TRACE3 for additional fine logging. This commit makes it possible
  to customize these levels on a per-project basis.

Backward compatibility notice: While there should be no issues
with backward compatibility and this should work completely out
of the box, please notice that, to align the code with syslog levels,
the values for the severity levels have been changed and now
lower values are considered more level.

Signed-off-by: Bojan Čekrlić verynotbad+github@gmail.com

[jujubot]

Can one of the admins verify this patch?

[jujubot]

Can one of the admins verify this patch?

[howbazaar]

I'm not a fan of adding more severity levels, or changing the ordering. Ordering mainly because we make use of this knowledge elsewhere.

Have you considered just working with a syslog writer? One that just does the value conversions when writing to syslog? I have vague recollections of one being written already.

[howbazaar]

For example, found this one: github.com/wolfeidau/loggo-syslog

[bokysan]

Hi,

https://github.com/wolfeidau/loggo-syslog will write to syslog, however, it will not support all logging levels offered by Syslog, because juju/loggo does not support them.

What this patch does is:

• add additional logging levels to keep them in live with what SYSLOG offers
• enables the user to add custom log levels, in much the same manner as it's possible in Java (e.g. https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Level.html)
• no additional methods (e.g. log.alert) have been added because I, too, believe that this is not necessary

I was a bit undecided, if ordering should be changed or not. In the end decided to go for it -- mostly because it makes more sense that the maximum level (EMERGENCY) is bound to a boundary. Another option would be to keep it as is and then have negative logging levels for new custom levels, which I think is a worse solution.

I have also verified where the log level code comparisons are used and all tests pass with this change.