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 [email protected]