Enhancement for Issue #1074. 

Added operator overload for pdnslog() to accept a log level when writing out to syslog. 
Added syslog levels to global lua table which correspond to the second argument in pdnslog. 
Moved pdns table instantiation to earlier in the constructor so it is globally accessible
Example: pdnslog("INFO", pdnslog.Info), pdnslog("DEBUG", pdnslog.Debug) , these all correspond to their name in the Urgency enum

Full pdns levels:
pdns.All
pdns.NTLog
pdns.Alert
pdns.Critical
pdns.Error
pdns.Warning
pdns.Notice
pdns.Info
pdns.Debug
pdns.None