Add support for "syslog" logging
Add support for syslog facilities local0-local7

The logging configuration now accepts strings "local0" through "local7"
as facility selectors.

The input is lowercased such that e.g. "LOCAL0" is valid, too.
Reformat code
Merge pull request #902 from malthe/add-syslog-handler

Add support for "syslog" logging